fix(play): absorb malformed HTML + warn when runner script is swallowed - #435
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Add `id="mdn-play-js"` and `id="mdn-play-js-end"` markers to the runner script and the script following it, and check from the head after `DOMContentLoaded` that both are present as script elements. If either is missing, log a console warning. Unclosed or malformed tags in the HTML input can absorb the runner script, so the JavaScript never executes and the playground silently does nothing. Mirrors mdn/fred.
Assert that the runner output carries the `mdn-play-js` and `mdn-play-js-end` markers and that the swallow detection runs from the `<head>` after `DOMContentLoaded`. Ported from `mdn/fred`, where the test lives outside the vendored directory.
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Insert `<!-- "" '' -->` after the HTML so an unclosed tag, attribute value, or comment ends there instead of swallowing the runner script. Set `window.__mdnPlayJsStarted` and `window.__mdnPlayJsEnded` around the runner and check those in `<head>`, since the script elements disappear when user JS replaces the body's children (a false positive in live samples using `document.body.innerHTML`).
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(⚠️ Mirrored from mdn/fred#1705. ⚠️ )
Description
Update the mirrored Playground runner (
cloud-function/src/internal/play/index.js) so malformed HTML no longer swallows the user's JS, and warn when it still does:<!-- "" '' -->after the HTML, which closes an unclosed tag, attribute value, or comment before the runner script.window.__mdnPlayJsStartedin a script before the runner andwindow.__mdnPlayJsEndedin the script after it.<head>check onDOMContentLoadedthat warns viaconsole.warnif either flag is missing.Ports the unit test from mdn/fred#1705 to
cloud-function/src/internal/play/index.test.js, next to the runner. The sync workflow only overwritesindex.js, so the test survives future syncs.Motivation
Ensure a typo like
<oin the HTML no longer renders the JS as text, and that users get a hint in the remaining cases (e.g. an unclosed<textarea>), where the JS silently does not run (mdn/fred#1440).This file serves the Playground runner in review and production, so the fix only takes effect outside local dev once this lands.
Additional details
Flags instead of marker elements: user JS that replaces the body's children (e.g.
document.body.innerHTML = ..., as several live samples do) removes the script elements but not the flags.Verified with headless Chrome:
<p>ok</p>annn <o jwj,<div class=", unclosed<!--document.bodychildren<textarea>,<template>,<math>Related issues and pull requests
Mirrors mdn/fred#1705, the fix for mdn/fred#1440.
Depends on: #437.