feat(interopDefault): support preferNamespace

README.md

@@ -469,6 +469,10 @@ import myModule from "my-module";
 console.log(interopDefault(myModule));
 ```
 
+**Options:**
+
+- `preferNamespace`: In case that `default` value exists but is not extendable (when is string for example), return input as-is (default is `false`, meaning `default`'s value is prefered even if cannot be extended)
+
 ### `sanitizeURIComponent`
 
 Replace reserved characters from a segment of URI to make it compatible with [rfc2396](https://datatracker.ietf.org/doc/html/rfc2396).

src/cjs.ts

@@ -31,7 +31,10 @@ export function createCommonJS(url: string): CommonjsContext {
   } as CommonjsContext;
 }
 
-export function interopDefault(sourceModule: any): any {
+export function interopDefault(
+  sourceModule: any,
+  opts: { preferNamespace?: boolean } = {},
+): any {
   if (!isObject(sourceModule) || !("default" in sourceModule)) {
     return sourceModule;
   }
@@ -40,7 +43,7 @@ export function interopDefault(sourceModule: any): any {
     return sourceModule;
   }
   if (typeof defaultValue !== "object") {
-    return defaultValue;
+    return opts.preferNamespace ? sourceModule : defaultValue;
   }
   for (const key in sourceModule) {
     if (key === "default") {

test/interop.test.ts

@@ -24,16 +24,26 @@ const tests = [
     { default: undefined, x: 1 },
     { default: undefined, x: 1 },
   ],
-];
+  [{ default: "test", x: 123 }, "test"],
+  [
+    { default: "test", x: 123 },
+    { default: "test", x: 123 },
+    { preferNamespace: true },
+  ],
+] as const;
 
 describe("interopDefault", () => {
-  for (const [input, result] of tests) {
+  for (const [input, result, opts] of tests) {
     it(JSON.stringify(input), () => {
-      const interop = interopDefault(input);
+      const interop = interopDefault(input, opts);
       expect(interop).to.deep.equal(result);
-      if (typeof input === "object" && "default" in input) {
+      if (
+        typeof input === "object" &&
+        typeof result === "object" &&
+        "default" in input
+      ) {
         expect(interop.default).to.deep.equal(
-          "default" in (result as any) ? (result as any).default : result,
+          "default" in result ? result.default : result,
         );
       } else {
         expect(interop).to.deep.equal(result);