Delete unused code from tex.ts (Khan#927)

## Summary:
There was a lot of code in this file related to our old KaTeX+MathJax2
renderer. Now that we have switched to MathJax 3, we can simplify things. I've
also deleted a couple functions that simply weren't used anywhere.

I changed the type of `processMath`'s `text` param to `string | number` because
the code that generates Graphie labels sometimes passes a number.

Issue: none

Test plan:

Review storybook stories that use TeX labels:

- Grapher widget
- Interactive Graph widget
- Number Line widget

The graph labels should display in the correct place.

Author: benchristel

Reviewers: benchristel, jeremywiebe

Required Reviewers:

Approved By: jeremywiebe

Checks: ✅ codecov/project, ✅ codecov/patch, ✅ Upload Coverage, ✅ Publish npm snapshot (ubuntu-latest, 20.x), ✅ Extract i18n strings (ubuntu-latest, 20.x), ✅ Lint, Typecheck, Format, and Test (ubuntu-latest, 20.x), ✅ Publish Storybook to Chromatic (ubuntu-latest, 20.x), ✅ Cypress (ubuntu-latest, 20.x), ✅ Jest Coverage (ubuntu-latest, 20.x), ✅ Check builds for changes in size (ubuntu-latest, 20.x), ✅ Check for .changeset entries for all changed files (ubuntu-latest, 20.x), ✅ gerald

Pull Request URL: Khan#927

.changeset/proud-donkeys-sip.md

@@ -0,0 +1,6 @@
+---
+"@khanacademy/perseus": patch
+---
+
+Remove unused code related to KaTeX and MathJax 2. It's no longer needed
+because all callers have upgraded to MathJax 3.

packages/perseus/src/util/tex.ts

@@ -6,8 +6,6 @@ import {getDependencies} from "../dependencies";
 import KhanMath from "./math";
 import reactRender from "./react-render";
 
-declare const MathJax: any;
-
 function findChildOrAdd(elem: any, className: string) {
     const $child = $(elem).find("." + className);
     if ($child.length === 0) {
@@ -16,27 +14,6 @@ function findChildOrAdd(elem: any, className: string) {
     return $child;
 }
 
-function doCallback(
-    elem: HTMLElement,
-    callback: (() => unknown) | (() => void),
-) {
-    let tries = 0;
-    (function check() {
-        const height = elem.scrollHeight;
-        // Heuristic to guess if the font has kicked in
-        // so we have box metrics (magic number ick,
-        // but this seems to work mostly-consistently)
-        if (height > 18 || tries >= 10) {
-            callback();
-        } else {
-            tries++;
-            // TODO(jeff, CP-3128): Use Wonder Blocks Timing API
-            // eslint-disable-next-line no-restricted-syntax
-            setTimeout(check, 100);
-        }
-    })();
-}
-
 export default {
     // Process a node and add math inside of it. This attempts to use KaTeX to
     // format the math, and if that fails it falls back to MathJax.
@@ -55,37 +32,22 @@ export default {
     //           processed
     processMath: async function (
         elem: HTMLElement,
-        text: string,
+        text: string | number,
         force?: boolean,
         callback?: () => unknown,
     ) {
         const $elem = $(elem);
 
         // Only process if it hasn't been done before, or it is forced
         if ($elem.attr("data-math-formula") == null || force) {
-            const $katexHolder = findChildOrAdd($elem, "katex-holder");
-            const $mathjaxHolder = findChildOrAdd($elem, "mathjax-holder");
-
-            // Search for MathJax-y script tags inside of the node. These are
-            // used by MathJax to denote the formula to be typeset. Before, we
-            // would update the formula by updating the contents of the script
-            // tag, which shouldn't happen any more, but we manage them just in
-            // case.
-            const script: HTMLElement | undefined = $mathjaxHolder.find(
-                "script[type='math/tex']",
-            )[0];
-
-            // If text wasn't provided, we look in two places
-            if (text == null) {
-                if ($elem.attr("data-math-formula")) {
-                    // The old typeset formula
-                    // @ts-expect-error - TS2322 - Type 'string | undefined' is not assignable to type 'string'.
-                    text = $elem.attr("data-math-formula");
-                } else if (script) {
-                    // The contents of the <script> tag
-                    // @ts-expect-error - TS2339 - Property 'text' does not exist on type 'HTMLElement'.
-                    text = script.text || script.textContent;
-                }
+            const $texHolder = findChildOrAdd($elem, "tex-holder");
+
+            // If text wasn't provided, we use the cached text.
+            // TODO(benchristel): I'm not sure if text can ever be null. It's
+            // possible we don't need this check.
+            if (text == null && $elem.attr("data-math-formula")) {
+                // @ts-expect-error - TS2322 - Type 'string | undefined' is not assignable to type 'string'.
+                text = $elem.attr("data-math-formula");
             }
 
             text = text != null ? text + "" : "";
@@ -102,45 +64,10 @@ export default {
             reactRender(
                 React.createElement(TeX, {
                     children: text,
-                    onRender: () => {
-                        if (callback) {
-                            doCallback(elem, callback);
-                        }
-                    },
+                    onRender: callback,
                 }),
-                $katexHolder[0],
+                $texHolder[0],
             );
         }
     },
-
-    // Function to restore a node to a non-math-processed state
-    cleanupMath: function (elem: HTMLElement): HTMLElement {
-        const $elem = $(elem);
-
-        // Only mess with it if it's been processed before
-        if ($elem.attr("data-math-formula")) {
-            // Remove MathJax remnants
-            if (typeof MathJax !== "undefined") {
-                const jax = MathJax.Hub.getJaxFor($elem.find("script")[0]);
-                if (jax) {
-                    const e = jax.SourceElement();
-                    if (e.previousSibling && e.previousSibling.className) {
-                        jax.Remove();
-                    }
-                }
-            }
-
-            // @ts-expect-error - TS2769 - No overload matches this call.
-            $elem.text($elem.attr("data-math-formula"));
-            $elem.attr("data-math-formula", null);
-            $elem.attr("data-math-type", null);
-        }
-
-        return elem;
-    },
-
-    // Function to retrieve the formula of a typeset math node
-    retrieveMathFormula: function (elem: HTMLElement): any {
-        return $(elem).attr("data-math-formula");
-    },
 };