diff --git a/hkmc2/jvm/src/test/scala/hkmc2/JSBackendDiffMaker.scala b/hkmc2/jvm/src/test/scala/hkmc2/JSBackendDiffMaker.scala
index d14737e39..edfffb7a4 100644
--- a/hkmc2/jvm/src/test/scala/hkmc2/JSBackendDiffMaker.scala
+++ b/hkmc2/jvm/src/test/scala/hkmc2/JSBackendDiffMaker.scala
@@ -13,12 +13,14 @@ import codegen.Block
 import codegen.js.Scope
 import hkmc2.syntax.Tree.Ident
 import hkmc2.codegen.Path
+import hkmc2.Diagnostic.Source
 
 abstract class JSBackendDiffMaker extends MLsDiffMaker:
   
   val debugLowering = NullaryCommand("dl")
   val js = NullaryCommand("js")
-  val sjs = NullaryCommand("sjs")
+  val showSanitizedJS = NullaryCommand("ssjs")
+  val showJS = NullaryCommand("sjs")
   val showRepl = NullaryCommand("showRepl")
   val silent = NullaryCommand("silent")
   val noSanityCheck = NullaryCommand("noSanityCheck")
@@ -49,7 +51,29 @@ abstract class JSBackendDiffMaker extends MLsDiffMaker:
   
   override def processTerm(blk: semantics.Term.Blk, inImport: Bool)(using Raise): Unit =
     super.processTerm(blk, inImport)
-    if js.isSet then
+    val outerRaise: Raise = summon
+    var showingJSYieldedCompileError = false
+    if showJS.isSet then
+      given Raise =
+        case d @ ErrorReport(source = Source.Compilation) =>
+          showingJSYieldedCompileError = true
+          outerRaise(d)
+        case d => outerRaise(d)
+      val low = ltl.givenIn:
+        new codegen.Lowering
+          with codegen.LoweringSelSanityChecks(instrument = false)
+          with codegen.LoweringTraceLog(instrument = false)
+      given Elaborator.Ctx = curCtx
+      val jsb = new JSBuilder
+        with JSBuilderArgNumSanityChecks(instrument = false)
+      val le = low.program(blk)
+      val nestedScp = baseScp.nest
+      val je = nestedScp.givenIn:
+        jsb.program(le, N, wd)
+      val jsStr = je.stripBreaks.mkString(100)
+      output(s"JS (unsanitized):")
+      output(jsStr)
+    if js.isSet && !showingJSYieldedCompileError then
       val low = ltl.givenIn:
         new codegen.Lowering
           with codegen.LoweringSelSanityChecks(noSanityCheck.isUnset)
@@ -71,7 +95,7 @@ abstract class JSBackendDiffMaker extends MLsDiffMaker:
       val je = nestedScp.givenIn:
         jsb.program(le, N, wd)
       val jsStr = je.stripBreaks.mkString(100)
-      if sjs.isSet then
+      if showSanitizedJS.isSet then
         output(s"JS:")
         output(jsStr)
       def mkQuery(prefix: Str, jsStr: Str) =
diff --git a/hkmc2/shared/src/main/scala/hkmc2/semantics/Elaborator.scala b/hkmc2/shared/src/main/scala/hkmc2/semantics/Elaborator.scala
index 20bda70ca..d56db3407 100644
--- a/hkmc2/shared/src/main/scala/hkmc2/semantics/Elaborator.scala
+++ b/hkmc2/shared/src/main/scala/hkmc2/semantics/Elaborator.scala
@@ -144,7 +144,8 @@ extends Importer:
         cls.definedSymbols.get(nme.name) match
         case s @ S(clsSym) => s
         case N =>
-          raise(ErrorReport(msg"Module '${cls.symbol.nme}' does not contain member '${nme.name}'" -> srcTree.toLoc :: Nil))
+          raise(ErrorReport(msg"${cls.k.desc.capitalize} '${cls.symbol.nme
+            }' does not contain member '${nme.name}'" -> srcTree.toLoc :: Nil))
           N
       case N =>
         N
diff --git a/hkmc2/shared/src/test/mlscript/basics/Classes.mls b/hkmc2/shared/src/test/mlscript/basics/Classes.mls
index 633cebad3..9371d1ad8 100644
--- a/hkmc2/shared/src/test/mlscript/basics/Classes.mls
+++ b/hkmc2/shared/src/test/mlscript/basics/Classes.mls
@@ -33,7 +33,7 @@ class Foo(x: Int) { log("Hello!") }
 //│ ╔══[ERROR] Expected a valid definition head, found block instead
 //│ ║  l.32: 	class Foo(x: Int) { log("Hello!") }
 //│ ╙──      	                    ^^^^^^^^^^^^^
-//│ JS:
+//│ JS (unsanitized):
 //│ this.<error> = class <error> { constructor() {  } toString() { return "<error>"; } }; null
 //│ > try { this.<error> = class <error> { constructor() {  } toString() { return "<error>"; } }; null } catch (e) { console.log('\u200B' + e + '\u200B'); }
 //│ >            ^
diff --git a/hkmc2/shared/src/test/mlscript/basics/MultiParamLists.mls b/hkmc2/shared/src/test/mlscript/basics/MultiParamLists.mls
index bfe257949..f33673a87 100644
--- a/hkmc2/shared/src/test/mlscript/basics/MultiParamLists.mls
+++ b/hkmc2/shared/src/test/mlscript/basics/MultiParamLists.mls
@@ -5,50 +5,28 @@
 
 
 fun f(n1: Int): Int = n1
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 1, true, args.length);
-//│   let n1 = args[0];
-//│   return n1;
-//│ }
-//│ null
+//│ JS (unsanitized):
+//│ function f(n1) { return n1; } null
 
 f(42)
-//│ JS:
+//│ JS (unsanitized):
 //│ this.f(42)
 //│ = 42
 
 fun f(n1: Int)(n2: Int): Int =  (10 * n1 + n2)
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 1, true, args.length);
-//│   let n1 = args[0];
-//│   return (...args1) => {
-//│     globalThis.Predef.checkArgs("", 1, true, args1.length);
-//│     let n2 = args1[0];
-//│     let tmp;
-//│     tmp = 10 * n1;
-//│     return tmp + n2;
-//│   };
-//│ }
-//│ null
+//│ JS (unsanitized):
+//│ function f(n1) { return (n2) => { let tmp; tmp = 10 * n1; return tmp + n2; }; } null
 
 f(4)(2)
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp; tmp = this.f(4); tmp(2) ?? null
 //│ = 42
 
 fun f(n1: Int)(n2: Int)(n3: Int): Int = 10 * (10 * n1 + n2) + n3
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 1, true, args.length);
-//│   let n1 = args[0];
-//│   return (...args1) => {
-//│     globalThis.Predef.checkArgs("", 1, true, args1.length);
-//│     let n2 = args1[0];
-//│     return (...args2) => {
-//│       globalThis.Predef.checkArgs("", 1, true, args2.length);
-//│       let n3 = args2[0];
+//│ JS (unsanitized):
+//│ function f(n1) {
+//│   return (n2) => {
+//│     return (n3) => {
 //│       let tmp, tmp1, tmp2;
 //│       tmp = 10 * n1;
 //│       tmp1 = tmp + n2;
@@ -60,24 +38,16 @@ fun f(n1: Int)(n2: Int)(n3: Int): Int = 10 * (10 * n1 + n2) + n3
 //│ null
 
 f(4)(2)(0)
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp, tmp1; tmp = this.f(4); tmp1 = tmp(2) ?? null; tmp1(0) ?? null
 //│ = 420
 
 fun f(n1: Int)(n2: Int)(n3: Int)(n4: Int): Int = 10 * (10 * (10 * n1 + n2) + n3) + n4
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 1, true, args.length);
-//│   let n1 = args[0];
-//│   return (...args1) => {
-//│     globalThis.Predef.checkArgs("", 1, true, args1.length);
-//│     let n2 = args1[0];
-//│     return (...args2) => {
-//│       globalThis.Predef.checkArgs("", 1, true, args2.length);
-//│       let n3 = args2[0];
-//│       return (...args3) => {
-//│         globalThis.Predef.checkArgs("", 1, true, args3.length);
-//│         let n4 = args3[0];
+//│ JS (unsanitized):
+//│ function f(n1) {
+//│   return (n2) => {
+//│     return (n3) => {
+//│       return (n4) => {
 //│         let tmp, tmp1, tmp2, tmp3, tmp4;
 //│         tmp = 10 * n1;
 //│         tmp1 = tmp + n2;
@@ -92,7 +62,7 @@ fun f(n1: Int)(n2: Int)(n3: Int)(n4: Int): Int = 10 * (10 * (10 * n1 + n2) + n3)
 //│ null
 
 f(3)(0)(3)(1)
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp, tmp1, tmp2; tmp = this.f(3); tmp1 = tmp(0) ?? null; tmp2 = tmp1(3) ?? null; tmp2(1) ?? null
 //│ = 3031
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/BadInit.mls b/hkmc2/shared/src/test/mlscript/codegen/BadInit.mls
index 0b5a3671a..4811fa65f 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/BadInit.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/BadInit.mls
@@ -8,20 +8,13 @@ module Bar with
   val x = 1
   module Baz with
     val a = Bar.x
-//│ JS:
+//│ JS (unsanitized):
 //│ const Bar$class = class Bar {
 //│   constructor() {
 //│     this.x = 1;
 //│     const Baz$class = class Baz {
 //│       constructor() {
-//│         let selRes, tmp;
-//│         selRes = globalThis.Bar.x;
-//│         if (selRes === undefined) {
-//│           throw new globalThis.Error("Access to required field 'x' yielded 'undefined'");
-//│         } else {
-//│           tmp = selRes;
-//│         }
-//│         this.a = tmp;
+//│         this.a = globalThis.Bar.x;
 //│       }
 //│       toString() { return "Baz"; }
 //│     };
diff --git a/hkmc2/shared/src/test/mlscript/codegen/BadNew.mls b/hkmc2/shared/src/test/mlscript/codegen/BadNew.mls
index 6c9390917..205aede86 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/BadNew.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/BadNew.mls
@@ -15,9 +15,8 @@ new 2
 :ge
 new 2 + 2
 //│ ═══[COMPILATION ERROR] Illegal reference to builtin symbol '+'
-//│ JS:
+//│ JS (unsanitized):
 //│ new (()=>{throw globalThis.Error("Illegal reference to builtin symbol '+'")})()(2, 2)
-//│ ═══[RUNTIME ERROR] TypeError: (intermediate value) is not a constructor
 
 :re
 new()
@@ -40,7 +39,7 @@ new { x = 1 }
 //│     lhs = Ident of "x"
 //│     rhs = IntLit of 1
 //│ ╔══[ERROR] Name not found: x
-//│ ║  l.36: 	new { x = 1 }
+//│ ║  l.35: 	new { x = 1 }
 //│ ╙──      	      ^
 
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/BadOpen.mls b/hkmc2/shared/src/test/mlscript/codegen/BadOpen.mls
index a1e747b7b..4807000aa 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/BadOpen.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/BadOpen.mls
@@ -23,7 +23,7 @@ open Foo { y }
 
 :sjs
 y
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Foo.y
 
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/BasicTerms.mls b/hkmc2/shared/src/test/mlscript/codegen/BasicTerms.mls
index 594c91883..035ff60a4 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/BasicTerms.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/BasicTerms.mls
@@ -5,7 +5,7 @@
 
 
 1
-//│ JS:
+//│ JS (unsanitized):
 //│ 1
 //│ = 1
 
@@ -16,20 +16,23 @@
 //│ ╔══[WARNING] Pure expression in statement position
 //│ ║  l.14: 	1
 //│ ╙──      	^
+//│ JS (unsanitized):
+//│ 2
+//│ ╔══[WARNING] Pure expression in statement position
+//│ ║  l.14: 	1
+//│ ╙──      	^
 //│ Lowered:
 //│ Program:
 //│   imports = Nil
 //│   main = Return:
 //│     res = Lit of IntLit of 2
 //│     implct = true
-//│ JS:
-//│ 2
 //│ = 2
 
 
 :fixme // should be a "linking" error
 log("Hi")
-//│ JS:
+//│ JS (unsanitized):
 //│ this.log("Hi") ?? null
 //│ ═══[RUNTIME ERROR] TypeError: this.log is not a function
 
@@ -37,6 +40,8 @@ log("Hi")
 :lot
 log("Hi")
 2
+//│ JS (unsanitized):
+//│ let tmp; tmp = this.log("Hi") ?? null; 2
 //│ Lowered:
 //│ Program:
 //│   imports = Nil
@@ -53,14 +58,12 @@ log("Hi")
 //│     rest = Return: \
 //│     res = Lit of IntLit of 2
 //│     implct = true
-//│ JS:
-//│ let tmp; tmp = this.log("Hi") ?? null; 2
 //│ ═══[RUNTIME ERROR] TypeError: this.log is not a function
 
 
 :re
 2(2)
-//│ JS:
+//│ JS (unsanitized):
 //│ 2(2) ?? null
 //│ ═══[RUNTIME ERROR] TypeError: 2 is not a function
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/BuiltinOps.mls b/hkmc2/shared/src/test/mlscript/codegen/BuiltinOps.mls
index ce5ec9e06..6cacd1f19 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/BuiltinOps.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/BuiltinOps.mls
@@ -3,19 +3,19 @@
 
 :sjs
 2 + 2
-//│ JS:
+//│ JS (unsanitized):
 //│ 2 + 2
 //│ = 4
 
 :sjs
 2 +. 2
-//│ JS:
+//│ JS (unsanitized):
 //│ 2 + 2
 //│ = 4
 
 :sjs
 +2
-//│ JS:
+//│ JS (unsanitized):
 //│ + 2
 //│ = 2
 
@@ -24,7 +24,7 @@ fun (+) lol(a, b) = [a, b]
 
 :sjs
 1 + 2
-//│ JS:
+//│ JS (unsanitized):
 //│ this.lol(1, 2)
 //│ = [ 1, 2 ]
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/CaseOfCase.mls b/hkmc2/shared/src/test/mlscript/codegen/CaseOfCase.mls
index 044290da2..751c7c205 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/CaseOfCase.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/CaseOfCase.mls
@@ -17,10 +17,8 @@ fun test(x) =
   ) is
     Some(v) then log(v)
     None then log("none")
-//│ JS:
-//│ function test(...args) {
-//│   globalThis.Predef.checkArgs("test", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ function test(x) {
 //│   let param0, v, scrut, param01, v1, tmp, tmp1;
 //│   if (x instanceof globalThis.Some.class) {
 //│     param0 = x.value;
diff --git a/hkmc2/shared/src/test/mlscript/codegen/CaseShorthand.mls b/hkmc2/shared/src/test/mlscript/codegen/CaseShorthand.mls
index 27bf7d1d9..4d8f448be 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/CaseShorthand.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/CaseShorthand.mls
@@ -10,38 +10,22 @@ case x then x
 
 :sjs
 case { x then x }
-//│ JS:
-//│ (...args) => {
-//│   globalThis.Predef.checkArgs("", 1, true, args.length);
-//│   let caseScrut = args[0];
-//│   let x;
-//│   x = caseScrut;
-//│   return x;
-//│ }
+//│ JS (unsanitized):
+//│ (caseScrut) => { let x; x = caseScrut; return x; }
 //│ = [Function (anonymous)]
 
 :sjs
 x => if x is
   0 then true
-//│ JS:
-//│ (...args) => {
-//│   globalThis.Predef.checkArgs("", 1, true, args.length);
-//│   let x = args[0];
-//│   if (x === 0) {
-//│     return true;
-//│   } else {
-//│     throw new this.Error("match error");
-//│   }
-//│ }
+//│ JS (unsanitized):
+//│ (x) => { if (x === 0) { return true; } else { throw new this.Error("match error"); } }
 //│ = [Function (anonymous)]
 
 :sjs
 case
   0 then true
-//│ JS:
-//│ (...args) => {
-//│   globalThis.Predef.checkArgs("", 1, true, args.length);
-//│   let caseScrut = args[0];
+//│ JS (unsanitized):
+//│ (caseScrut) => {
 //│   if (caseScrut === 0) {
 //│     return true;
 //│   } else {
@@ -54,16 +38,8 @@ case
 case
   0 then true
   _ then false
-//│ JS:
-//│ (...args) => {
-//│   globalThis.Predef.checkArgs("", 1, true, args.length);
-//│   let caseScrut = args[0];
-//│   if (caseScrut === 0) {
-//│     return true;
-//│   } else {
-//│     return false;
-//│   }
-//│ }
+//│ JS (unsanitized):
+//│ (caseScrut) => { if (caseScrut === 0) { return true; } else { return false; } }
 //│ = [Function (anonymous)]
 
 class Some(value)
@@ -73,10 +49,8 @@ module None
 val isDefined = case
   Some then true
   None then false
-//│ JS:
-//│ this.isDefined = (...args) => {
-//│   globalThis.Predef.checkArgs("", 1, true, args.length);
-//│   let caseScrut = args[0];
+//│ JS (unsanitized):
+//│ this.isDefined = (caseScrut) => {
 //│   if (caseScrut instanceof this.Some.class) {
 //│     return true;
 //│   } else {
diff --git a/hkmc2/shared/src/test/mlscript/codegen/ClassInClass.mls b/hkmc2/shared/src/test/mlscript/codegen/ClassInClass.mls
index fcc70e08a..234a5af8b 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/ClassInClass.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/ClassInClass.mls
@@ -16,28 +16,26 @@ class Outer(a, b) with
   val i = Inner(a)
   log(i.c)
   log(i.i1(1))
-//│ JS:
-//│ this.Outer = function Outer(...args) { return new Outer.class(...args); };
+//│ JS (unsanitized):
+//│ this.Outer = function Outer(a1, b1) { return new Outer.class(a1, b1); };
 //│ this.Outer.class = class Outer {
 //│   constructor(a, b) {
 //│     this.a = a;
 //│     this.b = b;
-//│     let tmp, selRes, tmp1, tmp2, tmp3;
+//│     let tmp, tmp1, tmp2;
 //│     
 //│     const this$Outer = this;
-//│     this.Inner = function Inner(...args1) { return new Inner.class(...args1); };
+//│     this.Inner = function Inner(c1) { return new Inner.class(c1); };
 //│     this.Inner.class = class Inner {
 //│       constructor(c) {
 //│         this.c = c;
-//│         let tmp4, tmp5, tmp6;
-//│         tmp4 = globalThis.log(this$Outer.a);
-//│         tmp5 = globalThis.log(this.c);
-//│         tmp6 = this.i1(this$Outer.a);
-//│         globalThis.log(tmp6)
+//│         let tmp3, tmp4, tmp5;
+//│         tmp3 = globalThis.log(this$Outer.a);
+//│         tmp4 = globalThis.log(this.c);
+//│         tmp5 = this.i1(this$Outer.a);
+//│         globalThis.log(tmp5)
 //│       }
-//│       i1(...args) {
-//│         globalThis.Predef.checkArgs("i1", 1, true, args.length);
-//│         let d = args[0];
+//│       i1(d) {
 //│         return [
 //│           this$Outer.b,
 //│           this.c,
@@ -48,25 +46,14 @@ class Outer(a, b) with
 //│     };
 //│     tmp = this.Inner(this.a);
 //│     this.i = tmp;
-//│     selRes = this.i.c;
-//│     if (selRes === undefined) {
-//│       throw new globalThis.Error("Access to required field 'c' yielded 'undefined'");
-//│     } else {
-//│       tmp1 = selRes;
-//│     }
-//│     tmp2 = globalThis.log(tmp1);
-//│     tmp3 = this.i.i1(1) ?? null;
-//│     globalThis.log(tmp3)
+//│     tmp1 = globalThis.log(this.i.c);
+//│     tmp2 = this.i.i1(1) ?? null;
+//│     globalThis.log(tmp2)
 //│   }
-//│   o1(...args) {
-//│     globalThis.Predef.checkArgs("o1", 1, true, args.length);
-//│     let c = args[0];
+//│   o1(c) {
 //│     return this.Inner(c);
 //│   } 
-//│   o2(...args1) {
-//│     globalThis.Predef.checkArgs("o2", 2, true, args1.length);
-//│     let c1 = args1[0];
-//│     let d = args1[1];
+//│   o2(c1, d) {
 //│     let tmp;
 //│     tmp = this.Inner(c1);
 //│     return tmp.i1(d) ?? null;
diff --git a/hkmc2/shared/src/test/mlscript/codegen/ClassInFun.mls b/hkmc2/shared/src/test/mlscript/codegen/ClassInFun.mls
index 185b4f5fc..e44d2183f 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/ClassInFun.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/ClassInFun.mls
@@ -8,10 +8,8 @@
 fun test(a) =
   class C with { val x = a }
   new C
-//│ JS:
-//│ function test(...args) {
-//│   globalThis.Predef.checkArgs("test", 1, true, args.length);
-//│   let a = args[0];
+//│ JS (unsanitized):
+//│ function test(a) {
 //│   class C {
 //│     constructor() {
 //│       this.x = a;
@@ -30,12 +28,10 @@ test(12)
 fun test(x) =
   class Foo(a, b)
   Foo(x, x + 1)
-//│ JS:
-//│ function test(...args) {
-//│   globalThis.Predef.checkArgs("test", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ function test(x) {
 //│   let tmp;
-//│   function Foo(...args1) { return new Foo.class(...args1); };
+//│   function Foo(a1, b1) { return new Foo.class(a1, b1); };
 //│   Foo.class = class Foo {
 //│     constructor(a, b) {
 //│       this.a = a;
diff --git a/hkmc2/shared/src/test/mlscript/codegen/ClassMatching.mls b/hkmc2/shared/src/test/mlscript/codegen/ClassMatching.mls
index 8dfa0c421..cb65c98d6 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/ClassMatching.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/ClassMatching.mls
@@ -11,7 +11,7 @@ object None
 
 :sjs
 if Some(0) is Some(x) then x
-//│ JS:
+//│ JS (unsanitized):
 //│ let scrut, param0, x;
 //│ scrut = this.Some(0);
 //│ if (scrut instanceof this.Some.class) {
@@ -30,7 +30,7 @@ let s = Some(0)
 :sjs
 if s is
   Some(x) then x
-//│ JS:
+//│ JS (unsanitized):
 //│ let scrut, param0, x;
 //│ scrut = this.s;
 //│ if (scrut instanceof this.Some.class) {
@@ -60,10 +60,8 @@ if s is
 
 :sjs
 x => if x is Some(x) then x
-//│ JS:
-//│ (...args) => {
-//│   globalThis.Predef.checkArgs("", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ (x) => {
 //│   let param0, x1;
 //│   if (x instanceof this.Some.class) {
 //│     param0 = x.value;
@@ -121,10 +119,8 @@ fun f(x) = if x is
   Some(x) and x > 0 then 42
   None then "ok"
   else log("oops")
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ function f(x) {
 //│   let param0, x1, scrut;
 //│   if (x instanceof globalThis.Some.class) {
 //│     param0 = x.value;
@@ -165,10 +161,8 @@ class Pair[out A, out B](fst: A, snd: B)
 fun f(x) = if x is
   Some(u) then u
   Pair(a, b) then a + b
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ function f(x) {
 //│   let param0, param1, a, b, param01, u;
 //│   if (x instanceof globalThis.Some.class) {
 //│     param01 = x.value;
@@ -201,10 +195,8 @@ fun f(x) = log of if x is
   Some(0) then "0"
   None then "ok"
   else "oops"
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ function f(x) {
 //│   let param0, tmp;
 //│   if (x instanceof globalThis.Some.class) {
 //│     param0 = x.value;
diff --git a/hkmc2/shared/src/test/mlscript/codegen/Comma.mls b/hkmc2/shared/src/test/mlscript/codegen/Comma.mls
index 90150bb0a..e034dabd8 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/Comma.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/Comma.mls
@@ -6,32 +6,16 @@
 
 fun f() =
   console.log("ok"), 42
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 0, true, args.length);
-//│   let tmp;
-//│   tmp = globalThis.console.log("ok") ?? null;
-//│   return 42;
-//│ }
-//│ null
+//│ JS (unsanitized):
+//│ function f() { let tmp; tmp = globalThis.console.log("ok") ?? null; return 42; } null
 
 fun f() = { console.log("ok"), 42 }
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 0, true, args.length);
-//│   let tmp;
-//│   tmp = globalThis.console.log("ok") ?? null;
-//│   return 42;
-//│ }
-//│ null
+//│ JS (unsanitized):
+//│ function f() { let tmp; tmp = globalThis.console.log("ok") ?? null; return 42; } null
 
 fun f() = console.log("ok"), 42
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 0, true, args.length);
-//│   return globalThis.console.log("ok") ?? null;
-//│ }
-//│ 42
+//│ JS (unsanitized):
+//│ function f() { return globalThis.console.log("ok") ?? null; } 42
 //│ = 42
 
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/ConsoleLog.mls b/hkmc2/shared/src/test/mlscript/codegen/ConsoleLog.mls
index dfb05a715..b5dfe98ba 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/ConsoleLog.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/ConsoleLog.mls
@@ -6,14 +6,14 @@
 
 :silent
 declare val console
-//│ JS:
+//│ JS (unsanitized):
 //│ null
 
 
 console.log("a")
 console.log("b")
 123
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp, tmp1; tmp = this.console.log("a") ?? null; tmp1 = this.console.log("b") ?? null; 123
 //│ > a
 //│ > b
@@ -21,27 +21,19 @@ console.log("b")
 
 let l = console.log
 l(123)
-//│ JS:
-//│ let selRes, tmp;
-//│ selRes = this.console.log;
-//│ if (selRes === undefined) {
-//│   throw new this.Error("Access to required field 'log' yielded 'undefined'");
-//│ } else {
-//│   tmp = selRes;
-//│ }
-//│ this.l = tmp;
-//│ this.l(123) ?? null
+//│ JS (unsanitized):
+//│ this.l = this.console.log; this.l(123) ?? null
 //│ > 123
 //│ l = [Function: log]
 
 42
-//│ JS:
+//│ JS (unsanitized):
 //│ 42
 //│ = 42
 
 
 console.log("a")
-//│ JS:
+//│ JS (unsanitized):
 //│ this.console.log("a") ?? null
 //│ > a
 
@@ -53,7 +45,7 @@ console.log("b")
 let y = x + 1
 console.log("c")
 y * 2
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp, tmp1, tmp2, tmp3;
 //│ tmp = this.console.log("a") ?? null;
 //│ this.x = 123;
diff --git a/hkmc2/shared/src/test/mlscript/codegen/DelayedLetInit.mls b/hkmc2/shared/src/test/mlscript/codegen/DelayedLetInit.mls
index dfecf723d..463537c2d 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/DelayedLetInit.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/DelayedLetInit.mls
@@ -5,31 +5,31 @@
 
 
 let x
-//│ JS:
+//│ JS (unsanitized):
 //│ null
 
 x = 1
-//│ JS:
+//│ JS (unsanitized):
 //│ this.x = 1; null
 
 x
-//│ JS:
+//│ JS (unsanitized):
 //│ this.x
 //│ = 1
 
 // TODO forbid redefining a let
 x = 2
-//│ JS:
+//│ JS (unsanitized):
 //│ this.x = 2; null
 
 x
-//│ JS:
+//│ JS (unsanitized):
 //│ this.x
 //│ = 2
 
 
 let y = 1
-//│ JS:
+//│ JS (unsanitized):
 //│ this.y = 1; null
 //│ y = 1
 
@@ -38,44 +38,35 @@ z = 1
 //│ ╔══[ERROR] Name not found: z
 //│ ║  l.37: 	z = 1
 //│ ╙──      	^
-//│ JS:
+//│ JS (unsanitized):
 //│ /* error */
 
 
 fun f() = 1
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 0, true, args.length);
-//│   return 1;
-//│ }
-//│ null
+//│ JS (unsanitized):
+//│ function f() { return 1; } null
 
 f
-//│ JS:
+//│ JS (unsanitized):
 //│ this.f
 //│ = [Function: f]
 
 
 let f
 f(x) = x + 1
-//│ JS:
-//│ this.f = (...args) => {
-//│   globalThis.Predef.checkArgs("", 1, true, args.length);
-//│   let x = args[0];
-//│   return x + 1;
-//│ };
-//│ null
+//│ JS (unsanitized):
+//│ this.f = (x) => { return x + 1; }; null
 //│ f = [Function (anonymous)]
 
 f(1)
-//│ JS:
+//│ JS (unsanitized):
 //│ this.f(1) ?? null
 //│ = 2
 
 
 let foo
 foo = 0
-//│ JS:
+//│ JS (unsanitized):
 //│ this.foo = 0; null
 //│ foo = 0
 
@@ -85,9 +76,9 @@ if true
 then foo = 0
 else foo = 1
 //│ ╔══[PARSE ERROR] Expected end of input; found '=' keyword instead
-//│ ║  l.85: 	then foo = 0
+//│ ║  l.76: 	then foo = 0
 //│ ╙──      	         ^
-//│ JS:
+//│ JS (unsanitized):
 //│ let scrut; scrut = true; if (scrut) { this.foo } else { throw new this.Error("match error"); }
 //│ = 0
 //│ foo = 0
@@ -98,27 +89,22 @@ then
   foo = 0
 else
   foo = 1
-//│ JS:
+//│ JS (unsanitized):
 //│ let scrut; scrut = true; if (scrut) { this.foo = 0; null } else { this.foo = 1; null }
 //│ foo = 0
 
 
 fun f() =
   foo = 42
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 0, true, args.length);
-//│   globalThis.foo = 42;
-//│   return null;
-//│ }
-//│ null
+//│ JS (unsanitized):
+//│ function f() { globalThis.foo = 42; return null; } null
 
 f()
-//│ JS:
+//│ JS (unsanitized):
 //│ this.f()
 
 foo
-//│ JS:
+//│ JS (unsanitized):
 //│ this.foo
 //│ = 42
 
@@ -126,13 +112,9 @@ foo
 :fixme
 fun f() = foo = 0
 //│ ╔══[PARSE ERROR] Expected end of input; found '=' keyword instead
-//│ ║  l.127: 	fun f() = foo = 0
+//│ ║  l.113: 	fun f() = foo = 0
 //│ ╙──       	              ^
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 0, true, args.length);
-//│   return globalThis.foo;
-//│ }
-//│ null
+//│ JS (unsanitized):
+//│ function f() { return globalThis.foo; } null
 
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/EarlyReturn.mls b/hkmc2/shared/src/test/mlscript/codegen/EarlyReturn.mls
index 6dc7950cd..61037077a 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/EarlyReturn.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/EarlyReturn.mls
@@ -20,10 +20,8 @@ fun f(x) =
     log("whoops")
     return 0
   x + 1
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ function f(x) {
 //│   let scrut, tmp, tmp1;
 //│   scrut = x < 0;
 //│   if (scrut) {
diff --git a/hkmc2/shared/src/test/mlscript/codegen/FunInClass.mls b/hkmc2/shared/src/test/mlscript/codegen/FunInClass.mls
index 2096e0265..317af5748 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/FunInClass.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/FunInClass.mls
@@ -21,34 +21,26 @@ fun test(a) =
       fun h(e) = [a, b, d, e]
       h(d)
   Inner(42)
-//│ JS:
-//│ function test(...args) {
-//│   globalThis.Predef.checkArgs("test", 1, true, args.length);
-//│   let a = args[0];
-//│   function Inner(...args1) { return new Inner.class(...args1); };
+//│ JS (unsanitized):
+//│ function test(a) {
+//│   function Inner(b1) { return new Inner.class(b1); };
 //│   Inner.class = class Inner {
 //│     constructor(b) {
 //│       this.b = b;
 //│       let tmp;
 //│       tmp = globalThis.log(a);
 //│     }
-//│     f(...args1) {
-//│       globalThis.Predef.checkArgs("f", 1, true, args1.length);
-//│       let c = args1[0];
+//│     f(c) {
 //│       return [
 //│         a,
 //│         this.b,
 //│         c
 //│       ];
 //│     } 
-//│     g(...args2) {
-//│       globalThis.Predef.checkArgs("g", 1, true, args2.length);
-//│       let d = args2[0];
+//│     g(d) {
 //│       
 //│       const this$Inner = this;
-//│       function h(...args1) {
-//│         globalThis.Predef.checkArgs("h", 1, true, args1.length);
-//│         let e = args1[0];
+//│       function h(e) {
 //│         return [
 //│           a,
 //│           this$Inner.b,
@@ -82,12 +74,10 @@ fun test(a) =
   class C2(b) with
     print of [a, b]
   [C1(1), C2(2)]
-//│ JS:
-//│ function test(...args) {
-//│   globalThis.Predef.checkArgs("test", 1, true, args.length);
-//│   let a = args[0];
+//│ JS (unsanitized):
+//│ function test(a) {
 //│   let tmp, tmp1;
-//│   function C1(...args1) { return new C1.class(...args1); };
+//│   function C1(b1) { return new C1.class(b1); };
 //│   C1.class = class C1 {
 //│     constructor(b) {
 //│       this.b = b;
@@ -98,7 +88,7 @@ fun test(a) =
 //│     }
 //│     toString() { return "C1(" + this.b + ")"; }
 //│   };
-//│   function C2(...args1) { return new C2.class(...args1); };
+//│   function C2(b1) { return new C2.class(b1); };
 //│   C2.class = class C2 {
 //│     constructor(b) {
 //│       this.b = b;
@@ -133,24 +123,21 @@ class Foo(a) with
     baz()
   foo()
 Foo(123)
-//│ JS:
-//│ this.Foo = function Foo(...args1) { return new Foo.class(...args1); };
+//│ JS (unsanitized):
+//│ this.Foo = function Foo(a1) { return new Foo.class(a1); };
 //│ this.Foo.class = class Foo {
 //│   constructor(a) {
 //│     this.a = a;
 //│     this.foo()
 //│   }
-//│   foo(...args) {
-//│     globalThis.Predef.checkArgs("foo", 0, true, args.length);
+//│   foo() {
 //│     let tmp;
 //│     
 //│     const this$Foo = this;
-//│     function bar(...args1) {
-//│       globalThis.Predef.checkArgs("bar", 0, true, args1.length);
+//│     function bar() {
 //│       return this$Foo.a;
 //│     }
-//│     function baz(...args1) {
-//│       globalThis.Predef.checkArgs("baz", 0, true, args1.length);
+//│     function baz() {
 //│       return this$Foo.a;
 //│     }
 //│     tmp = bar();
diff --git a/hkmc2/shared/src/test/mlscript/codegen/FunctionsThis.mls b/hkmc2/shared/src/test/mlscript/codegen/FunctionsThis.mls
index c5ece633c..a1da1cee9 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/FunctionsThis.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/FunctionsThis.mls
@@ -8,19 +8,14 @@
 val x = 2
 fun foo() =
   x + 1
-//│ JS:
-//│ this.x = 2;
-//│ function foo(...args) {
-//│   globalThis.Predef.checkArgs("foo", 0, true, args.length);
-//│   return globalThis.x + 1;
-//│ }
-//│ null
+//│ JS (unsanitized):
+//│ this.x = 2; function foo() { return globalThis.x + 1; } null
 //│ x = 2
 
 :sjs
 class Test with
   log(foo())
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Test = class Test {
 //│   constructor() {
 //│     let tmp;
diff --git a/hkmc2/shared/src/test/mlscript/codegen/GlobalThis.mls b/hkmc2/shared/src/test/mlscript/codegen/GlobalThis.mls
index 192b86a00..f99b0fe27 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/GlobalThis.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/GlobalThis.mls
@@ -17,7 +17,7 @@ globalThis
 :sjs
 :re
 if false then 0
-//│ JS:
+//│ JS (unsanitized):
 //│ let scrut; scrut = false; if (scrut) { 0 } else { throw new this.Error("match error"); }
 //│ ═══[RUNTIME ERROR] Error: match error
 
@@ -28,9 +28,8 @@ if false then 0
 fun foo() =
   if false then 0
 foo()
-//│ JS:
-//│ function foo(...args) {
-//│   globalThis.Predef.checkArgs("foo", 0, true, args.length);
+//│ JS (unsanitized):
+//│ function foo() {
 //│   let scrut;
 //│   scrut = false;
 //│   if (scrut) {
diff --git a/hkmc2/shared/src/test/mlscript/codegen/Hygiene.mls b/hkmc2/shared/src/test/mlscript/codegen/Hygiene.mls
index b187e5c1c..2767cd506 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/Hygiene.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/Hygiene.mls
@@ -5,20 +5,13 @@
 module Test with
   val x = 12
   fun foo() = Test.x
-//│ JS:
+//│ JS (unsanitized):
 //│ const Test$class = class Test {
 //│   constructor() {
 //│     this.x = 12;
 //│   }
-//│   foo(...args) {
-//│     globalThis.Predef.checkArgs("foo", 0, true, args.length);
-//│     let selRes;
-//│     selRes = globalThis.Test.x;
-//│     if (selRes === undefined) {
-//│       throw new globalThis.Error("Access to required field 'x' yielded 'undefined'");
-//│     } else {
-//│       return selRes;
-//│     }
+//│   foo() {
+//│     return globalThis.Test.x;
 //│   }
 //│   toString() { return "Test"; }
 //│ };
@@ -28,13 +21,13 @@ module Test with
 
 :sjs
 Test.foo()
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Test.foo()
 //│ = 12
 
 :sjs
 val Test = "oops"
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Test = "oops"; null
 //│ Test = 'oops'
 
@@ -49,14 +42,8 @@ let x = 1
 let f = () => x
 let x = 2
 f()
-//│ JS:
-//│ this.x = 1;
-//│ this.f = (...args) => {
-//│   globalThis.Predef.checkArgs("", 0, true, args.length);
-//│   return this.x;
-//│ };
-//│ this.x = 2;
-//│ this.f() ?? null
+//│ JS (unsanitized):
+//│ this.x = 1; this.f = () => { return this.x; }; this.x = 2; this.f() ?? null
 //│ = 2
 //│ f = [Function (anonymous)]
 //│ x = 2
@@ -66,7 +53,7 @@ f()
 module Test with
   val x = 1
   let x = 2
-//│ JS:
+//│ JS (unsanitized):
 //│ const Test$class = class Test {
 //│   #x;
 //│   constructor() {
diff --git a/hkmc2/shared/src/test/mlscript/codegen/IfThenElse.mls b/hkmc2/shared/src/test/mlscript/codegen/IfThenElse.mls
index 065e682ce..278b23789 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/IfThenElse.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/IfThenElse.mls
@@ -11,17 +11,8 @@ if true then 1 else 0
 
 :sjs
 let f = x => if x then log("ok") else log("ko")
-//│ JS:
-//│ this.f = (...args) => {
-//│   globalThis.Predef.checkArgs("", 1, true, args.length);
-//│   let x = args[0];
-//│   if (x) {
-//│     return this.log("ok");
-//│   } else {
-//│     return this.log("ko");
-//│   }
-//│ };
-//│ null
+//│ JS (unsanitized):
+//│ this.f = (x) => { if (x) { return this.log("ok"); } else { return this.log("ko"); } }; null
 //│ f = [Function (anonymous)]
 
 f(true)
@@ -33,10 +24,8 @@ f(false)
 
 :sjs
 let f = x => log((if x then "ok" else "ko") + "!")
-//│ JS:
-//│ this.f = (...args) => {
-//│   globalThis.Predef.checkArgs("", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ this.f = (x) => {
 //│   let tmp, tmp1;
 //│   if (x) {
 //│     tmp = "ok";
@@ -51,10 +40,8 @@ let f = x => log((if x then "ok" else "ko") + "!")
 
 :sjs
 let f = x => log((if x and x then "ok" else "ko") + "!")
-//│ JS:
-//│ this.f = (...args) => {
-//│   globalThis.Predef.checkArgs("", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ this.f = (x) => {
 //│   let tmp, tmp1;
 //│   if (x) {
 //│     if (x) {
diff --git a/hkmc2/shared/src/test/mlscript/codegen/ImportExample.mls b/hkmc2/shared/src/test/mlscript/codegen/ImportExample.mls
index 7f44e519c..62d7461b5 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/ImportExample.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/ImportExample.mls
@@ -17,7 +17,7 @@ let n = 42
 
 :sjs
 n / 2
-//│ JS:
+//│ JS (unsanitized):
 //│ this.n / 2
 //│ = 21
 
@@ -28,14 +28,14 @@ open Example
 
 :sjs
 inc / 2
-//│ JS:
+//│ JS (unsanitized):
 //│ Example.funnySlash(Example.inc, 2)
 //│ = 3
 
 :sjs
 :re
 n / 2
-//│ JS:
+//│ JS (unsanitized):
 //│ Example.funnySlash(this.n, 2)
 //│ ═══[RUNTIME ERROR] TypeError: f is not a function
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/ImportMLs.mls b/hkmc2/shared/src/test/mlscript/codegen/ImportMLs.mls
index 7977c81e8..b3a59ada7 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/ImportMLs.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/ImportMLs.mls
@@ -23,7 +23,7 @@ open Option
 
 :sjs
 None isDefined()
-//│ JS:
+//│ JS (unsanitized):
 //│ Option.isDefined(Option.None)
 //│ = false
 
@@ -46,7 +46,7 @@ Some(1)
 
 :sjs
 (new Some(1)) isDefined()
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp; tmp = new Option.Some.class(1); Option.isDefined(tmp)
 //│ = true
 
@@ -91,7 +91,7 @@ oops
 :e
 :re
 Option.None.oops
-//│ ╔══[ERROR] Module 'None' does not contain member 'oops'
+//│ ╔══[ERROR] Object 'None' does not contain member 'oops'
 //│ ║  l.93: 	Option.None.oops
 //│ ╙──      	           ^^^^^
 //│ ═══[RUNTIME ERROR] Error: Access to required field 'oops' yielded 'undefined'
diff --git a/hkmc2/shared/src/test/mlscript/codegen/ImportedOps.mls b/hkmc2/shared/src/test/mlscript/codegen/ImportedOps.mls
index 64a16b55d..c551c63a6 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/ImportedOps.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/ImportedOps.mls
@@ -10,9 +10,8 @@ open M
 fun foo() =
   "a" ~ "b" ~ "c"
 foo()
-//│ JS:
-//│ function foo(...args) {
-//│   globalThis.Predef.checkArgs("foo", 0, true, args.length);
+//│ JS (unsanitized):
+//│ function foo() {
 //│   let tmp;
 //│   tmp = globalThis.M.concat("a", "b");
 //│   return globalThis.M.concat(tmp, "c");
diff --git a/hkmc2/shared/src/test/mlscript/codegen/Lambdas.mls b/hkmc2/shared/src/test/mlscript/codegen/Lambdas.mls
index 121b0ac4e..8bc695bad 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/Lambdas.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/Lambdas.mls
@@ -7,14 +7,8 @@
 x =>
   let y = x
   y
-//│ JS:
-//│ (...args) => {
-//│   globalThis.Predef.checkArgs("", 1, true, args.length);
-//│   let x = args[0];
-//│   let y;
-//│   y = x;
-//│   return y;
-//│ }
+//│ JS (unsanitized):
+//│ (x) => { let y; y = x; return y; }
 //│ = [Function (anonymous)]
 
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/Misc.mls b/hkmc2/shared/src/test/mlscript/codegen/Misc.mls
index 7e31562cc..6cec30897 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/Misc.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/Misc.mls
@@ -14,7 +14,7 @@
 :sjs
 1 +
 2
-//│ JS:
+//│ JS (unsanitized):
 //│ 1 + 2
 //│ = 3
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/ModuleMethods.mls b/hkmc2/shared/src/test/mlscript/codegen/ModuleMethods.mls
index 853cf7b5e..e9852a5cf 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/ModuleMethods.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/ModuleMethods.mls
@@ -6,14 +6,12 @@
 object Example with
   val a = 456
   fun f(x) = [x, a]
-//│ JS:
+//│ JS (unsanitized):
 //│ const Example$class = class Example {
 //│   constructor() {
 //│     this.a = 456;
 //│   }
-//│   f(...args) {
-//│     globalThis.Predef.checkArgs("f", 1, true, args.length);
-//│     let x = args[0];
+//│   f(x) {
 //│     return [
 //│       x,
 //│       this.a
diff --git a/hkmc2/shared/src/test/mlscript/codegen/Modules.mls b/hkmc2/shared/src/test/mlscript/codegen/Modules.mls
index 6cdc3c9cd..3a03e4171 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/Modules.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/Modules.mls
@@ -6,7 +6,7 @@
 
 :sjs
 module None
-//│ JS:
+//│ JS (unsanitized):
 //│ const None$class = class None {
 //│   constructor() {
 //│     
@@ -19,20 +19,20 @@ module None
 
 :sjs
 None
-//│ JS:
+//│ JS (unsanitized):
 //│ this.None
 //│ = None { class: [class None] }
 
 :sjs
 :re
 None()
-//│ JS:
+//│ JS (unsanitized):
 //│ this.None() ?? null
 //│ ═══[RUNTIME ERROR] TypeError: this.None is not a function
 
 :sjs
 new None
-//│ JS:
+//│ JS (unsanitized):
 //│ new this.None.class()
 //│ = None {}
 
@@ -43,7 +43,7 @@ module M with
   class D()
   val x = 1
   val y = x + 1
-//│ JS:
+//│ JS (unsanitized):
 //│ const M$class = class M {
 //│   constructor() {
 //│     let tmp;
@@ -53,7 +53,7 @@ module M with
 //│       }
 //│       toString() { return "C"; }
 //│     };
-//│     this.D = function D(...args) { return new D.class(...args); };
+//│     this.D = function D() { return new D.class(); };
 //│     this.D.class = class D {
 //│       constructor() {
 //│         
@@ -97,7 +97,7 @@ M.oops
 :sjs
 module M with
   val m: module M = M
-//│ JS:
+//│ JS (unsanitized):
 //│ const M$class = class M {
 //│   constructor() {
 //│     this.m = globalThis.M;
diff --git a/hkmc2/shared/src/test/mlscript/codegen/Open.mls b/hkmc2/shared/src/test/mlscript/codegen/Open.mls
index c0edf285b..4d016a0cd 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/Open.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/Open.mls
@@ -8,7 +8,7 @@ module Foo with
 
 :sjs
 open Foo { x }
-//│ JS:
+//│ JS (unsanitized):
 //│ null
 
 open Foo { x, y }
diff --git a/hkmc2/shared/src/test/mlscript/codegen/OpenWildcard.mls b/hkmc2/shared/src/test/mlscript/codegen/OpenWildcard.mls
index 5aae4cf39..1e66663ea 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/OpenWildcard.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/OpenWildcard.mls
@@ -9,12 +9,12 @@ module OtherModule with
 
 :sjs
 open Option
-//│ JS:
+//│ JS (unsanitized):
 //│ null
 
 :sjs
 None isDefined()
-//│ JS:
+//│ JS (unsanitized):
 //│ Option.isDefined(Option.None)
 //│ = false
 
@@ -51,14 +51,14 @@ none()
 
 :sjs
 val Option = "Oops"
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Option = "Oops"; null
 //│ Option = 'Oops'
 
 :fixme
 :sjs
 Some(123)
-//│ JS:
+//│ JS (unsanitized):
 //│ Option.Some(123)
 //│ ═══[RUNTIME ERROR] TypeError: Option.Some is not a function
 
@@ -67,17 +67,17 @@ module Option with
 
 :sjs
 open Option
-//│ JS:
+//│ JS (unsanitized):
 //│ null
 
 :sjs
 Some
-//│ JS:
+//│ JS (unsanitized):
 //│ Option.Some
 
 :sjs
 None
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Option.None
 //│ = 123
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/OptMatch.mls b/hkmc2/shared/src/test/mlscript/codegen/OptMatch.mls
index a727be9fc..689c05615 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/OptMatch.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/OptMatch.mls
@@ -9,10 +9,8 @@ object None
 fun isDefined(x) = if x is
   Some then true
   None then false
-//│ JS:
-//│ function isDefined(...args) {
-//│   globalThis.Predef.checkArgs("isDefined", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ function isDefined(x) {
 //│   if (x instanceof globalThis.Some.class) {
 //│     return true;
 //│   } else {
@@ -36,10 +34,8 @@ isDefined(None)
 val isDefined = case
   Some(_) then true
   None    then false
-//│ JS:
-//│ this.isDefined = (...args) => {
-//│   globalThis.Predef.checkArgs("", 1, true, args.length);
-//│   let caseScrut = args[0];
+//│ JS (unsanitized):
+//│ this.isDefined = (caseScrut) => {
 //│   let param0;
 //│   if (caseScrut instanceof this.Some.class) {
 //│     param0 = caseScrut.value;
diff --git a/hkmc2/shared/src/test/mlscript/codegen/ParamClasses.mls b/hkmc2/shared/src/test/mlscript/codegen/ParamClasses.mls
index c96aa5a94..86b431247 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/ParamClasses.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/ParamClasses.mls
@@ -8,8 +8,8 @@
 
 
 class Foo()
-//│ JS:
-//│ this.Foo = function Foo(...args) { return new Foo.class(...args); };
+//│ JS (unsanitized):
+//│ this.Foo = function Foo() { return new Foo.class(); };
 //│ this.Foo.class = class Foo {
 //│   constructor() {
 //│     
@@ -19,30 +19,24 @@ class Foo()
 //│ null
 
 Foo
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Foo
 //│ = [Function: Foo] { class: [class Foo] }
 
 Foo()
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Foo()
 //│ = Foo {}
 
 Foo.class
-//│ JS:
-//│ let selRes;
-//│ selRes = this.Foo.class;
-//│ if (selRes === undefined) {
-//│   throw new this.Error("Access to required field 'class' yielded 'undefined'");
-//│ } else {
-//│   selRes
-//│ }
+//│ JS (unsanitized):
+//│ this.Foo.class
 //│ = [class Foo]
 
 
 class Foo(a)
-//│ JS:
-//│ this.Foo = function Foo(...args) { return new Foo.class(...args); };
+//│ JS (unsanitized):
+//│ this.Foo = function Foo(a1) { return new Foo.class(a1); };
 //│ this.Foo.class = class Foo {
 //│   constructor(a) {
 //│     this.a = a;
@@ -53,42 +47,30 @@ class Foo(a)
 //│ null
 
 Foo
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Foo
 //│ = [Function: Foo] { class: [class Foo] }
 
 Foo(1)
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Foo(1)
 //│ = Foo { a: 1 }
 
 Foo(1).a
-//│ JS:
-//│ let tmp, selRes;
-//│ tmp = this.Foo(1);
-//│ selRes = tmp.a;
-//│ if (selRes === undefined) {
-//│   throw new this.Error("Access to required field 'a' yielded 'undefined'");
-//│ } else {
-//│   selRes
-//│ }
+//│ JS (unsanitized):
+//│ let tmp; tmp = this.Foo(1); tmp.a
 //│ = 1
 
 fun foo(y) = Foo(y)
 foo(27)
-//│ JS:
-//│ function foo(...args) {
-//│   globalThis.Predef.checkArgs("foo", 1, true, args.length);
-//│   let y = args[0];
-//│   return globalThis.Foo(y);
-//│ }
-//│ this.foo(27)
+//│ JS (unsanitized):
+//│ function foo(y) { return globalThis.Foo(y); } this.foo(27)
 //│ = Foo { a: 27 }
 
 
 class Foo(a, b)
-//│ JS:
-//│ this.Foo = function Foo(...args) { return new Foo.class(...args); };
+//│ JS (unsanitized):
+//│ this.Foo = function Foo(a1, b1) { return new Foo.class(a1, b1); };
 //│ this.Foo.class = class Foo {
 //│   constructor(a, b) {
 //│     this.a = a;
@@ -100,71 +82,47 @@ class Foo(a, b)
 //│ null
 
 let foo = Foo
-//│ JS:
+//│ JS (unsanitized):
 //│ this.foo = this.Foo; null
 //│ foo = [Function: Foo] { class: [class Foo] }
 
 let f = foo(1, 2)
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp; tmp = this.foo(1, 2) ?? null; this.f = tmp; null
 //│ f = Foo { a: 1, b: 2 }
 
 let f = new foo(1, 2)
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp; tmp = new this.foo(1, 2); this.f = tmp; null
 //│ f = Foo { a: 1, b: 2 }
 
 f.a
-//│ JS:
-//│ let selRes;
-//│ selRes = this.f.a;
-//│ if (selRes === undefined) {
-//│   throw new this.Error("Access to required field 'a' yielded 'undefined'");
-//│ } else {
-//│   selRes
-//│ }
+//│ JS (unsanitized):
+//│ this.f.a
 //│ = 1
 
 f.b
-//│ JS:
-//│ let selRes;
-//│ selRes = this.f.b;
-//│ if (selRes === undefined) {
-//│   throw new this.Error("Access to required field 'b' yielded 'undefined'");
-//│ } else {
-//│   selRes
-//│ }
+//│ JS (unsanitized):
+//│ this.f.b
 //│ = 2
 
 let f = Foo(1, 2)
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp; tmp = this.Foo(1, 2); this.f = tmp; null
 //│ f = Foo { a: 1, b: 2 }
 
 f.a
-//│ JS:
-//│ let selRes;
-//│ selRes = this.f.a;
-//│ if (selRes === undefined) {
-//│   throw new this.Error("Access to required field 'a' yielded 'undefined'");
-//│ } else {
-//│   selRes
-//│ }
+//│ JS (unsanitized):
+//│ this.f.a
 //│ = 1
 
 f.b
-//│ JS:
-//│ let selRes;
-//│ selRes = this.f.b;
-//│ if (selRes === undefined) {
-//│   throw new this.Error("Access to required field 'b' yielded 'undefined'");
-//│ } else {
-//│   selRes
-//│ }
+//│ JS (unsanitized):
+//│ this.f.b
 //│ = 2
 
 Foo(log(1), log(2))
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp, tmp1; tmp = this.log(1); tmp1 = this.log(2); this.Foo(tmp, tmp1)
 //│ > 1
 //│ > 2
@@ -174,16 +132,14 @@ Foo(log(1), log(2))
 class Inner(c) with
   fun i1(d) = c + d
   log(c)
-//│ JS:
-//│ this.Inner = function Inner(...args1) { return new Inner.class(...args1); };
+//│ JS (unsanitized):
+//│ this.Inner = function Inner(c1) { return new Inner.class(c1); };
 //│ this.Inner.class = class Inner {
 //│   constructor(c) {
 //│     this.c = c;
 //│     globalThis.log(this.c)
 //│   }
-//│   i1(...args) {
-//│     globalThis.Predef.checkArgs("i1", 1, true, args.length);
-//│     let d = args[0];
+//│   i1(d) {
 //│     return this.c + d;
 //│   }
 //│   toString() { return "Inner(" + this.c + ")"; }
@@ -191,13 +147,13 @@ class Inner(c) with
 //│ null
 
 let i = new Inner(100)
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp; tmp = new this.Inner.class(100); this.i = tmp; null
 //│ > 100
 //│ i = Inner { c: 100 }
 
 i.i1(20)
-//│ JS:
+//│ JS (unsanitized):
 //│ this.i.i1(20) ?? null
 //│ = 120
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/PlainClasses.mls b/hkmc2/shared/src/test/mlscript/codegen/PlainClasses.mls
index 550cefee9..0b72eaedc 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/PlainClasses.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/PlainClasses.mls
@@ -8,44 +8,44 @@
 
 
 class Foo
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Foo = class Foo { constructor() {  } toString() { return "Foo"; } }; null
 
 Foo is Foo
-//│ JS:
+//│ JS (unsanitized):
 //│ let scrut; scrut = this.Foo; if (scrut instanceof this.Foo) { true } else { false }
 //│ = false
 
 (new Foo) is Foo
-//│ JS:
+//│ JS (unsanitized):
 //│ let scrut; scrut = new this.Foo(); if (scrut instanceof this.Foo) { true } else { false }
 //│ = true
 
 new Foo
-//│ JS:
+//│ JS (unsanitized):
 //│ new this.Foo()
 //│ = Foo {}
 
 new Foo()
-//│ JS:
+//│ JS (unsanitized):
 //│ new this.Foo()
 //│ = Foo {}
 
 Foo
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Foo
 //│ = [class Foo]
 
 :re
 Foo()
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Foo()
 //│ ═══[RUNTIME ERROR] TypeError: Class constructor Foo cannot be invoked without 'new'
 
 
 class Foo with { log("hi") }
 log("ok")
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Foo = class Foo {
 //│   constructor() {
 //│     globalThis.log("hi")
@@ -59,9 +59,8 @@ fun test() =
   class Foo with { log("hi") }
   log("ok")
   Foo
-//│ JS:
-//│ function test(...args) {
-//│   globalThis.Predef.checkArgs("test", 0, true, args.length);
+//│ JS (unsanitized):
+//│ function test() {
 //│   let tmp;
 //│   class Foo {
 //│     constructor() {
@@ -75,19 +74,19 @@ fun test() =
 //│ null
 
 let t = test()
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp; tmp = this.test(); this.t = tmp; null
 //│ > ok
 //│ t = [class Foo]
 
 new t
-//│ JS:
+//│ JS (unsanitized):
 //│ new this.t()
 //│ > hi
 //│ = Foo {}
 
 new t()
-//│ JS:
+//│ JS (unsanitized):
 //│ new this.t()
 //│ > hi
 //│ = Foo {}
@@ -97,7 +96,7 @@ class Foo with
   val x = 1
   let y = x + 1
   fun z() = y + x
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Foo = class Foo {
 //│   #y;
 //│   constructor() {
@@ -106,8 +105,7 @@ class Foo with
 //│     tmp = this.x + 1;
 //│     this.#y = tmp;
 //│   }
-//│   z(...args) {
-//│     globalThis.Predef.checkArgs("z", 0, true, args.length);
+//│   z() {
 //│     return this.#y + this.x;
 //│   }
 //│   toString() { return "Foo"; }
@@ -123,7 +121,7 @@ class Foo with
   fun z1() = 5
   fun z2() = 6
   log("hello")
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Foo = class Foo {
 //│   #y1;
 //│   #y2;
@@ -134,12 +132,10 @@ class Foo with
 //│     this.#y2 = 4;
 //│     globalThis.log("hello")
 //│   }
-//│   z1(...args) {
-//│     globalThis.Predef.checkArgs("z1", 0, true, args.length);
+//│   z1() {
 //│     return 5;
 //│   } 
-//│   z2(...args1) {
-//│     globalThis.Predef.checkArgs("z2", 0, true, args1.length);
+//│   z2() {
 //│     return 6;
 //│   }
 //│   toString() { return "Foo"; }
@@ -151,19 +147,15 @@ class Foo with
   val x = 1
   fun foo(y) = x + y
   fun bar(z) = foo(z) + 1
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Foo = class Foo {
 //│   constructor() {
 //│     this.x = 1;
 //│   }
-//│   foo(...args) {
-//│     globalThis.Predef.checkArgs("foo", 1, true, args.length);
-//│     let y = args[0];
+//│   foo(y) {
 //│     return this.x + y;
 //│   } 
-//│   bar(...args1) {
-//│     globalThis.Predef.checkArgs("bar", 1, true, args1.length);
-//│     let z = args1[0];
+//│   bar(z) {
 //│     let tmp;
 //│     tmp = this.foo(z);
 //│     return tmp + 1;
@@ -176,21 +168,15 @@ let a = new Foo
 log(a.x)
 log(a.foo(1))
 log(a.bar(1))
-//│ JS:
-//│ let tmp, selRes, tmp1, tmp2, tmp3, tmp4, tmp5;
+//│ JS (unsanitized):
+//│ let tmp, tmp1, tmp2, tmp3, tmp4;
 //│ tmp = new this.Foo();
 //│ this.a = tmp;
-//│ selRes = this.a.x;
-//│ if (selRes === undefined) {
-//│   throw new this.Error("Access to required field 'x' yielded 'undefined'");
-//│ } else {
-//│   tmp1 = selRes;
-//│ }
-//│ tmp2 = this.log(tmp1);
-//│ tmp3 = this.a.foo(1) ?? null;
-//│ tmp4 = this.log(tmp3);
-//│ tmp5 = this.a.bar(1) ?? null;
-//│ this.log(tmp5)
+//│ tmp1 = this.log(this.a.x);
+//│ tmp2 = this.a.foo(1) ?? null;
+//│ tmp3 = this.log(tmp2);
+//│ tmp4 = this.a.bar(1) ?? null;
+//│ this.log(tmp4)
 //│ > 1
 //│ > 2
 //│ > 3
@@ -207,7 +193,7 @@ log(a.bar(1))
 class Foo with
   val x = 1
   let x = 2
-//│ JS:
+//│ JS (unsanitized):
 //│ this.Foo = class Foo {
 //│   #x;
 //│   constructor() {
@@ -222,15 +208,15 @@ class Foo with
 :fixme
 class Foo with val x = 1
 //│ ╔══[PARSE ERROR] Expected block after type declaration body; found 'val' keyword instead
-//│ ║  l.223: 	class Foo with val x = 1
+//│ ║  l.209: 	class Foo with val x = 1
 //│ ╙──       	               ^^^
 //│ ╔══[PARSE ERROR] Expected end of input; found '=' keyword instead
-//│ ║  l.223: 	class Foo with val x = 1
+//│ ║  l.209: 	class Foo with val x = 1
 //│ ╙──       	                     ^
 //│ ╔══[ERROR] Illegal juxtaposition right-hand side.
-//│ ║  l.223: 	class Foo with val x = 1
+//│ ║  l.209: 	class Foo with val x = 1
 //│ ╙──       	                   ^
-//│ JS:
+//│ JS (unsanitized):
 //│ /* error */
 
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/PredefUsage.mls b/hkmc2/shared/src/test/mlscript/codegen/PredefUsage.mls
index 05697bdbd..513b80910 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/PredefUsage.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/PredefUsage.mls
@@ -13,7 +13,7 @@ print(12)
 
 :sjs
 12 |> print
-//│ JS:
+//│ JS (unsanitized):
 //│ Predef.pipe(12, Predef.print)
 //│ > 12
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/Primes.mls b/hkmc2/shared/src/test/mlscript/codegen/Primes.mls
index 42518dc8e..9e77d55eb 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/Primes.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/Primes.mls
@@ -7,7 +7,7 @@ let x = 1
 :fixme
 :sjs
 let x' = 1
-//│ JS:
+//│ JS (unsanitized):
 //│ this.x' = 1; null
 //│ > try { this.x' = 1; null } catch (e) { console.log('\u200B' + e + '\u200B'); }
 //│ >             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/hkmc2/shared/src/test/mlscript/codegen/Pwd.mls b/hkmc2/shared/src/test/mlscript/codegen/Pwd.mls
index 5e715a994..fa9279704 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/Pwd.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/Pwd.mls
@@ -6,30 +6,18 @@
 let folderName1 = process.env.PWD.split("/").pop()
 in let folderName2 = process.cwd().split("/").pop()
 in folderName2 === folderName1 || folderName2 === "jvm"
-//│ JS:
-//│ let selRes, tmp, selRes1, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7, tmp8;
-//│ selRes = this.process.env;
-//│ if (selRes === undefined) {
-//│   throw new this.Error("Access to required field 'env' yielded 'undefined'");
-//│ } else {
-//│   tmp = selRes;
-//│ }
-//│ selRes1 = tmp.PWD;
-//│ if (selRes1 === undefined) {
-//│   throw new this.Error("Access to required field 'PWD' yielded 'undefined'");
-//│ } else {
-//│   tmp1 = selRes1;
-//│ }
-//│ tmp2 = tmp1.split("/") ?? null;
-//│ tmp3 = tmp2.pop() ?? null;
-//│ this.folderName1 = tmp3;
-//│ tmp4 = this.process.cwd() ?? null;
-//│ tmp5 = tmp4.split("/") ?? null;
-//│ tmp6 = tmp5.pop() ?? null;
-//│ this.folderName2 = tmp6;
-//│ tmp7 = this.folderName2 === this.folderName1;
-//│ tmp8 = this.folderName2 === "jvm";
-//│ tmp7 || tmp8
+//│ JS (unsanitized):
+//│ let tmp, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6;
+//│ tmp = this.process.env.PWD.split("/") ?? null;
+//│ tmp1 = tmp.pop() ?? null;
+//│ this.folderName1 = tmp1;
+//│ tmp2 = this.process.cwd() ?? null;
+//│ tmp3 = tmp2.split("/") ?? null;
+//│ tmp4 = tmp3.pop() ?? null;
+//│ this.folderName2 = tmp4;
+//│ tmp5 = this.folderName2 === this.folderName1;
+//│ tmp6 = this.folderName2 === "jvm";
+//│ tmp5 || tmp6
 //│ = true
 
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/SanityChecks.mls b/hkmc2/shared/src/test/mlscript/codegen/SanityChecks.mls
index c57eb3ab6..0e096fc9f 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/SanityChecks.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/SanityChecks.mls
@@ -2,7 +2,7 @@
 
 
 
-:sjs
+:ssjs
 fun f(x, y) = x + y
 f(2, 3)
 //│ JS:
@@ -17,7 +17,7 @@ f(2, 3)
 
 
 :expect NaN
-:sjs
+:ssjs
 :noSanityCheck
 fun f2(x, y) = x + y
 f2(2)
@@ -25,7 +25,7 @@ f2(2)
 //│ function f2(x, y) { return x + y; } this.f2(2)
 //│ = NaN
 
-:sjs
+:ssjs
 :re
 f(2)
 //│ JS:
@@ -33,7 +33,7 @@ f(2)
 //│ ═══[RUNTIME ERROR] Error: Function 'f' expected 2 arguments but got 1
 
 
-:sjs
+:ssjs
 :re
 fun f(x)(y, z) = x + y + z
 f(3)(4)
@@ -57,14 +57,14 @@ f(3)(4)
 
 
 :expect NaN
-:sjs
+:ssjs
 :noSanityCheck
 let f = (x, y) => x + y in f(2)
 //│ JS:
 //│ this.f = (x, y) => { return x + y; }; this.f(2) ?? null
 //│ = NaN
 
-:sjs
+:ssjs
 :re
 let f = (x, y) => x + y
 f(2)
@@ -81,7 +81,7 @@ f(2)
 
 
 :expect NaN
-:sjs
+:ssjs
 :noSanityCheck
 class Cls(x, y) with
   fun f(z, p) = x + y + z + p
@@ -107,7 +107,7 @@ Cls(1, 2).f(3)
 //│ tmp.f(3) ?? null
 //│ = NaN
 
-:sjs
+:ssjs
 :re
 class Cls(x, y) with
   fun f(z, p) = x + y + z + p
@@ -137,7 +137,7 @@ Cls(1, 2).f(3)
 //│ ═══[RUNTIME ERROR] Error: Function 'f' expected 2 arguments but got 1
 
 
-:sjs
+:ssjs
 :re
 class Cls(x, y) with
   fun f(z, p)(q, s) = x + y + z + p + q + s
@@ -175,7 +175,7 @@ Cls(1, 2).f(3, 4)(5)
 //│ ═══[RUNTIME ERROR] Error: Function expected 2 arguments but got 1
 
 
-:sjs
+:ssjs
 console.log(1)
 //│ JS:
 //│ this.console.log(1) ?? null
@@ -183,7 +183,7 @@ console.log(1)
 
 
 :re
-:sjs
+:ssjs
 globalThis.x
 //│ JS:
 //│ let selRes;
@@ -196,7 +196,7 @@ globalThis.x
 //│ ═══[RUNTIME ERROR] Error: Access to required field 'x' yielded 'undefined'
 
 :re
-:sjs
+:ssjs
 globalThis.x()
 //│ JS:
 //│ this.x() ?? null
@@ -206,7 +206,7 @@ globalThis.x()
 
 
 :re
-:sjs
+:ssjs
 module M with
   class A(x) with
     fun f(y) = x + y
@@ -254,7 +254,7 @@ if M.A(1).y is
 
 
 
-:sjs
+:ssjs
 :re
 M.A(1).y
   console.log()
@@ -272,7 +272,7 @@ M.A(1).y
 
 
 
-:sjs
+:ssjs
 :noSanityCheck
 M.A(1).y
   console.log()
@@ -290,7 +290,7 @@ M.A(2).y > 1
 //│ ═══[RUNTIME ERROR] Error: Access to required field 'y' yielded 'undefined'
 
 :re
-:sjs
+:ssjs
 M.A(1).g(0)
 //│ JS:
 //│ let tmp; tmp = this.M.A(1); tmp.g(0) ?? null
@@ -298,8 +298,11 @@ M.A(1).g(0)
 
 
 
-:sjs
+:ssjs
 M.A(1).f(0)
 //│ JS:
 //│ let tmp; tmp = this.M.A(1); tmp.f(0) ?? null
 //│ = 1
+
+
+
diff --git a/hkmc2/shared/src/test/mlscript/codegen/SetIn.mls b/hkmc2/shared/src/test/mlscript/codegen/SetIn.mls
index b1567a110..67c5f7e12 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/SetIn.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/SetIn.mls
@@ -9,7 +9,7 @@ let x = 0
 
 :sjs
 let x += 1
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp; tmp = this.x + 1; this.x = tmp; null
 //│ x = 1
 
@@ -18,12 +18,12 @@ x
 
 :sjs
 set x = 0
-//│ JS:
+//│ JS (unsanitized):
 //│ this.x = 0; null
 
 :sjs
 set x += 1
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp; tmp = this.x + 1; this.x = tmp; null
 
 x
@@ -32,7 +32,7 @@ x
 
 :sjs
 set x += 1 in log(x)
-//│ JS:
+//│ JS (unsanitized):
 //│ let old, tmp, tmp1;
 //│ old = this.x;
 //│ try {
@@ -77,13 +77,11 @@ fun example() =
   log(x)
   log(get_x())
 example()
-//│ JS:
-//│ function example(...args) {
-//│   globalThis.Predef.checkArgs("example", 0, true, args.length);
+//│ JS (unsanitized):
+//│ function example() {
 //│   let x, get_x, old, tmp, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6;
 //│   x = 0;
-//│   get_x = (...args1) => {
-//│     globalThis.Predef.checkArgs("", 0, true, args1.length);
+//│   get_x = () => {
 //│     return x;
 //│   };
 //│   old = x;
@@ -117,13 +115,11 @@ fun example() =
   log(get_x())
   y
 example()
-//│ JS:
-//│ function example(...args) {
-//│   globalThis.Predef.checkArgs("example", 0, true, args.length);
+//│ JS (unsanitized):
+//│ function example() {
 //│   let x, get_x, y, old, tmp, tmp1, tmp2, tmp3, tmp4, tmp5;
 //│   x = 0;
-//│   get_x = (...args1) => {
-//│     globalThis.Predef.checkArgs("", 0, true, args1.length);
+//│   get_x = () => {
 //│     return x;
 //│   };
 //│   old = x;
diff --git a/hkmc2/shared/src/test/mlscript/codegen/Spreads.mls b/hkmc2/shared/src/test/mlscript/codegen/Spreads.mls
index 0c59cc0cc..576c4c0f3 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/Spreads.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/Spreads.mls
@@ -18,7 +18,7 @@ foo(0, ...a)
 
 :sjs
 foo(1, ...[2, 3], 4)
-//│ JS:
+//│ JS (unsanitized):
 //│ this.foo(1, ...[ 2, 3 ], 4)
 //│ = [ 1, 2, 3, 4 ]
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/This.mls b/hkmc2/shared/src/test/mlscript/codegen/This.mls
index a88c75fe8..0ecb43a81 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/This.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/This.mls
@@ -4,23 +4,8 @@
 :sjs
 fun test(x) =
   [this.a, x]
-//│ JS:
-//│ function test(...args) {
-//│   globalThis.Predef.checkArgs("test", 1, true, args.length);
-//│   let x = args[0];
-//│   let selRes, tmp;
-//│   selRes = globalThis.a;
-//│   if (selRes === undefined) {
-//│     throw new globalThis.Error("Access to required field 'a' yielded 'undefined'");
-//│   } else {
-//│     tmp = selRes;
-//│   }
-//│   return [
-//│     tmp,
-//│     x
-//│   ];
-//│ }
-//│ null
+//│ JS (unsanitized):
+//│ function test(x) { return [ globalThis.a, x ]; } null
 
 :re
 test(123)
@@ -39,28 +24,17 @@ module Test with
     test(x)
   fun test2(x) =
     [this.a, x]
-//│ JS:
+//│ JS (unsanitized):
 //│ const Test$class = class Test {
 //│   constructor() {
 //│     this.a = 2;
 //│   }
-//│   test1(...args) {
-//│     globalThis.Predef.checkArgs("test1", 1, true, args.length);
-//│     let x = args[0];
+//│   test1(x) {
 //│     return globalThis.test(x);
 //│   } 
-//│   test2(...args1) {
-//│     globalThis.Predef.checkArgs("test2", 1, true, args1.length);
-//│     let x1 = args1[0];
-//│     let selRes, tmp;
-//│     selRes = this.a;
-//│     if (selRes === undefined) {
-//│       throw new globalThis.Error("Access to required field 'a' yielded 'undefined'");
-//│     } else {
-//│       tmp = selRes;
-//│     }
+//│   test2(x1) {
 //│     return [
-//│       tmp,
+//│       this.a,
 //│       x1
 //│     ];
 //│   }
diff --git a/hkmc2/shared/src/test/mlscript/codegen/ThisCallVariations.mls b/hkmc2/shared/src/test/mlscript/codegen/ThisCallVariations.mls
index 9bb52e769..dfa6ae1f7 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/ThisCallVariations.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/ThisCallVariations.mls
@@ -41,7 +41,7 @@ Example . oops(2)
 //│       Ident of "oops"
 //│   rhs = Tup of Ls of 
 //│     IntLit of 2
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp; tmp = this.call(this.Example, this.oops); tmp(2) ?? null
 //│ = [ 2, 1 ]
 
@@ -52,7 +52,7 @@ Example. oops(2)
 :e
 :re
 Example .oops(2)
-//│ ╔══[ERROR] Module 'Example' does not contain member 'oops'
+//│ ╔══[ERROR] Object 'Example' does not contain member 'oops'
 //│ ║  l.54: 	Example .oops(2)
 //│ ╙──      	        ^^^^^
 //│ ═══[RUNTIME ERROR] TypeError: this.Example.oops is not a function
@@ -99,7 +99,7 @@ Example .> oops(2)
 //│       lhs = Ident of "oops"
 //│       rhs = Tup of Ls of 
 //│         IntLit of 2
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp; tmp = this.oops(2) ?? null; this.call(this.Example, tmp)
 //│ = [Function (anonymous)]
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/ThisCalls.mls b/hkmc2/shared/src/test/mlscript/codegen/ThisCalls.mls
index cde7493a0..776a77ab5 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/ThisCalls.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/ThisCalls.mls
@@ -18,7 +18,7 @@ s(123)
 
 :sjs
 ex |>. s(123)
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp; tmp = Predef.call(this.ex, this.s); tmp(123) ?? null
 //│ = [ 123, 456 ]
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/Throw.mls b/hkmc2/shared/src/test/mlscript/codegen/Throw.mls
index 284b09fbb..69c61a6e9 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/Throw.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/Throw.mls
@@ -30,13 +30,8 @@ fun f(x) =
   let y = throw Error("e")
   return y
 f(1)
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 1, true, args.length);
-//│   let x = args[0];
-//│   throw globalThis.Error("e");
-//│ }
-//│ this.f(1)
+//│ JS (unsanitized):
+//│ function f(x) { throw globalThis.Error("e"); } this.f(1)
 //│ ═══[RUNTIME ERROR] Error: e
 
 
@@ -45,10 +40,8 @@ f(1)
 fun f(x) =
   throw (if x then Error("x") else Error("y"))
 f(false)
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ function f(x) {
 //│   if (x) {
 //│     throw globalThis.Error("x");
 //│   } else {
diff --git a/hkmc2/shared/src/test/mlscript/codegen/TraceLog.mls b/hkmc2/shared/src/test/mlscript/codegen/TraceLog.mls
index 2b0ac991f..d707589ed 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/TraceLog.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/TraceLog.mls
@@ -6,29 +6,19 @@
 fun fib(a) = if
   a <= 1 then a
   else fib(a - 1) + fib(a - 2)
-//│ JS:
+//│ JS (unsanitized):
 //│ function fib(a) {
-//│   let scrut, traceLogEnterMsg, traceLogPrevIndent, traceLogRes, traceLogRetMsg, traceLogParam_a, traceLogResInspected, tmp, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
-//│   traceLogParam_a = globalThis.util.inspect(a);
-//│   traceLogEnterMsg = globalThis.String.prototype.concat.call("CALL fib(", traceLogParam_a, ")");
-//│   tmp = globalThis.Predef.TraceLogger.log(traceLogEnterMsg);
-//│   traceLogPrevIndent = globalThis.Predef.TraceLogger.indent();
+//│   let scrut, tmp, tmp1, tmp2, tmp3;
 //│   scrut = a <= 1;
 //│   if (scrut) {
-//│     tmp1 = a;
+//│     return a;
 //│   } else {
-//│     tmp2 = a - 1;
+//│     tmp = a - 1;
+//│     tmp1 = globalThis.fib(tmp);
+//│     tmp2 = a - 2;
 //│     tmp3 = globalThis.fib(tmp2);
-//│     tmp4 = a - 2;
-//│     tmp5 = globalThis.fib(tmp4);
-//│     tmp1 = tmp3 + tmp5;
+//│     return tmp1 + tmp3;
 //│   }
-//│   traceLogRes = tmp1;
-//│   traceLogResInspected = globalThis.util.inspect(traceLogRes);
-//│   traceLogRetMsg = globalThis.String.prototype.concat.call("=> ", traceLogResInspected);
-//│   tmp6 = globalThis.Predef.TraceLogger.resetIndent(traceLogPrevIndent);
-//│   tmp7 = globalThis.Predef.TraceLogger.log(traceLogRetMsg);
-//│   return traceLogRes;
 //│ }
 //│ null
 
diff --git a/hkmc2/shared/src/test/mlscript/codegen/While.mls b/hkmc2/shared/src/test/mlscript/codegen/While.mls
index 3c31c6f3b..10fc2b7bc 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/While.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/While.mls
@@ -6,9 +6,8 @@
 
 :sjs
 () => (while true then 0)
-//│ JS:
-//│ (...args) => {
-//│   globalThis.Predef.checkArgs("", 0, true, args.length);
+//│ JS (unsanitized):
+//│ () => {
 //│   let scrut, tmp;
 //│   tmp1: while (true) {
 //│     scrut = true;
@@ -54,7 +53,7 @@ while x
     log("Hello World")
     set x = false
   else 42
-//│ JS:
+//│ JS (unsanitized):
 //│ let scrut, tmp, tmp1;
 //│ tmp2: while (true) {
 //│   scrut = this.x;
@@ -107,9 +106,8 @@ while log("checking"); i < 3
 while
   let i = 0
   i < 10 do set i += 1
-//│ JS:
-//│ (...args) => {
-//│   globalThis.Predef.checkArgs("", 0, true, args.length);
+//│ JS (unsanitized):
+//│ () => {
 //│   let i, scrut, tmp, tmp1;
 //│   tmp2: while (true) {
 //│     i = 0;
@@ -204,10 +202,8 @@ fun f(ls) =
       set ls = tl
       log(h)
   else log("Done!")
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 1, true, args.length);
-//│   let ls = args[0];
+//│ JS (unsanitized):
+//│ function f(ls) {
 //│   let param0, param1, h, tl, tmp;
 //│   tmp1: while (true) {
 //│     if (ls instanceof globalThis.Cons.class) {
@@ -264,7 +260,7 @@ while log("Hello World"); false
   then 0(0)
   else 1
 //│ ╔══[PARSE ERROR] Unexpected 'then' keyword here
-//│ ║  l.264: 	  then 0(0)
+//│ ║  l.260: 	  then 0(0)
 //│ ╙──       	  ^^^^
 //│ ═══[ERROR] Unrecognized term split (false literal).
 //│ > Hello World
diff --git a/hkmc2/shared/src/test/mlscript/parser/PrefixOps.mls b/hkmc2/shared/src/test/mlscript/parser/PrefixOps.mls
index 7c93263dd..a190d5672 100644
--- a/hkmc2/shared/src/test/mlscript/parser/PrefixOps.mls
+++ b/hkmc2/shared/src/test/mlscript/parser/PrefixOps.mls
@@ -18,8 +18,11 @@
 //│ ╔══[WARNING] Pure expression in statement position
 //│ ║  l.15: 	1
 //│ ╙──      	^
-//│ JS:
+//│ JS (unsanitized):
 //│ let tmp, tmp1; tmp = + 2; tmp1 = + 3; tmp1
+//│ ╔══[WARNING] Pure expression in statement position
+//│ ║  l.15: 	1
+//│ ╙──      	^
 //│ = 3
 
 :w
@@ -29,10 +32,10 @@
 * 2
 * 3
 //│ ╔══[PARSE ERROR] Expected end of input; found literal instead
-//│ ║  l.29: 	* 2
+//│ ║  l.32: 	* 2
 //│ ╙──      	  ^
 //│ ╔══[WARNING] Pure expression in statement position
-//│ ║  l.28: 	1
+//│ ║  l.31: 	1
 //│ ╙──      	^
 //│ ═══[COMPILATION ERROR] Illegal reference to builtin symbol '*'
 //│ ═══[RUNTIME ERROR] Error: Illegal reference to builtin symbol '*'
@@ -42,9 +45,8 @@
 :ge
 +
 //│ ═══[COMPILATION ERROR] Illegal reference to builtin symbol '+'
-//│ JS:
+//│ JS (unsanitized):
 //│ (()=>{throw globalThis.Error("Illegal reference to builtin symbol '+'")})()
-//│ ═══[RUNTIME ERROR] Error: Illegal reference to builtin symbol '+'
 
 :ge
 *
@@ -60,7 +62,7 @@
 //│ IntLit of 1
 //│ Ident of "*"
 //│ ╔══[WARNING] Pure expression in statement position
-//│ ║  l.57: 	1
+//│ ║  l.59: 	1
 //│ ╙──      	^
 //│ ═══[COMPILATION ERROR] Illegal reference to builtin symbol '*'
 //│ ═══[RUNTIME ERROR] Error: Illegal reference to builtin symbol '*'
@@ -90,7 +92,7 @@ fun (??) foo(x, y) = x + y
 :pe
 ?? 1
 //│ ╔══[PARSE ERROR] Expected end of input; found literal instead
-//│ ║  l.91: 	?? 1
+//│ ║  l.93: 	?? 1
 //│ ╙──      	   ^
 //│ = [Function: foo]
 
@@ -99,11 +101,11 @@ fun (??) foo(x, y) = x + y
 1
 ?? 2
 //│ ╔══[PARSE ERROR] Expected end of input; found literal instead
-//│ ║  l.100: 	?? 2
+//│ ║  l.102: 	?? 2
 //│ ╙──       	   ^
 //│ ╔══[WARNING] Pure expression in statement position
-//│ ║  l.99: 	1
-//│ ╙──      	^
+//│ ║  l.101: 	1
+//│ ╙──       	^
 //│ = [Function: foo]
 
 :fixme
diff --git a/hkmc2/shared/src/test/mlscript/rp/MatchResult.mls b/hkmc2/shared/src/test/mlscript/rp/MatchResult.mls
index 1e1067a9a..05fb9033e 100644
--- a/hkmc2/shared/src/test/mlscript/rp/MatchResult.mls
+++ b/hkmc2/shared/src/test/mlscript/rp/MatchResult.mls
@@ -27,10 +27,8 @@ Cross.unapply("0")
 
 :sjs
 fun foo(x) = x is Cross
-//│ JS:
-//│ function foo(...args) {
-//│   globalThis.Predef.checkArgs("foo", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ function foo(x) {
 //│   let matchResult;
 //│   matchResult = globalThis.Cross.unapply(x) ?? null;
 //│   if (matchResult instanceof globalThis.Predef.MatchResult.class) {
diff --git a/hkmc2/shared/src/test/mlscript/ucs/normalization/SimplePairMatches.mls b/hkmc2/shared/src/test/mlscript/ucs/normalization/SimplePairMatches.mls
index 2de7cb589..3cee46b46 100644
--- a/hkmc2/shared/src/test/mlscript/ucs/normalization/SimplePairMatches.mls
+++ b/hkmc2/shared/src/test/mlscript/ucs/normalization/SimplePairMatches.mls
@@ -8,10 +8,8 @@ class B
 
 :sjs
 x => if x is Pair(A, B) then 1
-//│ JS:
-//│ (...args) => {
-//│   globalThis.Predef.checkArgs("", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ (x) => {
 //│   let param0, param1;
 //│   if (x instanceof this.Pair.class) {
 //│     param0 = x.a;
@@ -37,10 +35,8 @@ x => if x is Pair(A, B) then 1
 fun f(x) = if x is
   Pair(A, A) then 1
   Pair(B, B) then 2
-//│ JS:
-//│ function f(...args) {
-//│   globalThis.Predef.checkArgs("f", 1, true, args.length);
-//│   let x = args[0];
+//│ JS (unsanitized):
+//│ function f(x) {
 //│   let param0, param1;
 //│   if (x instanceof globalThis.Pair.class) {
 //│     param0 = x.a;
diff --git a/hkmc2/shared/src/test/mlscript/ucs/patterns/RestTuple.mls b/hkmc2/shared/src/test/mlscript/ucs/patterns/RestTuple.mls
index 507066c49..b64d9798f 100644
--- a/hkmc2/shared/src/test/mlscript/ucs/patterns/RestTuple.mls
+++ b/hkmc2/shared/src/test/mlscript/ucs/patterns/RestTuple.mls
@@ -16,10 +16,8 @@ tupleGet([1, 2, 3, 4], -1)
 fun nonsense(xs) = if xs is
   [..ys] then ys
   [] then "empty"
-//│ JS:
-//│ function nonsense(...args) {
-//│   globalThis.Predef.checkArgs("nonsense", 1, true, args.length);
-//│   let xs = args[0];
+//│ JS (unsanitized):
+//│ function nonsense(xs) {
 //│   let rest, ys;
 //│   if (globalThis.Array.isArray(xs) && xs.length >= 0) {
 //│     rest = globalThis.Predef.tupleSlice(xs, 0, 0) ?? null;
@@ -41,10 +39,8 @@ nonsense([1, 2, 3, 4])
 fun lead_and_last(xs) = if xs is
   [x, ..ys, y] then x + y
   [] then 0
-//│ JS:
-//│ function lead_and_last(...args) {
-//│   globalThis.Predef.checkArgs("lead_and_last", 1, true, args.length);
-//│   let xs = args[0];
+//│ JS (unsanitized):
+//│ function lead_and_last(xs) {
 //│   let last0, rest, first0, x, ys, y;
 //│   if (globalThis.Array.isArray(xs) && xs.length >= 2) {
 //│     first0 = xs[0];
@@ -81,10 +77,8 @@ lead_and_last(["boom"])
 fun nested_tuple_patterns(xs) = if xs is
   [x, ..[y, z], w] then x + y + z + w
   [] then 0
-//│ JS:
-//│ function nested_tuple_patterns(...args) {
-//│   globalThis.Predef.checkArgs("nested_tuple_patterns", 1, true, args.length);
-//│   let xs = args[0];
+//│ JS (unsanitized):
+//│ function nested_tuple_patterns(xs) {
 //│   let last0, rest, first0, x, first1, first01, y, z, w, tmp, tmp1;
 //│   if (globalThis.Array.isArray(xs) && xs.length >= 2) {
 //│     first0 = xs[0];