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fix(playground): absorb malformed HTML + warn when runner script is swallowed #1705

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fix(playground): absorb malformed HTML + warn when runner script is swallowed #1705

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ede933b
fix(playground): warn when malformed HTML swallows the runner script
caugner Sep 3, 2026
138b9be
fix(playground): absorb malformed HTML + track runner execution via f…
caugner Sep 9, 2026
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54 changes: 54 additions & 0 deletions test/unit/play/runner.test.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,54 @@
import assert from "node:assert/strict";
import { describe, it } from "node:test";

import { renderHtml } from "../../../vendor/yari/libs/play/index.js";

describe("play renderHtml", () => {
const out = renderHtml({ html: "<p>ok</p>", css: "", js: "1;" });
const body = out.slice(out.indexOf("<body>"));
const head = out.slice(0, out.indexOf("</head>"));

const cases = [
{
name: "closes unclosed tags, attribute values, and comments",
haystack: body,
needle: `<!-- "" '' -->`,
},
{
name: "records that the runner script was reached",
haystack: body,
needle: "window.__mdnPlayJsStarted = true;",
},
{
name: "records that the runner script ended",
haystack: body,
needle: "window.__mdnPlayJsEnded = true;",
},
{
name: "checks the flags from the head",
haystack: head,
needle: "window.__mdnPlayJsStarted && window.__mdnPlayJsEnded",
},
{
name: "checks the flags after DOMContentLoaded",
haystack: head,
needle: 'addEventListener("DOMContentLoaded"',
},
];

for (const { name, haystack, needle } of cases) {
it(name, () => {
assert.ok(haystack.includes(needle), `missing ${needle}`);
});
}

it("places the closer and flag script between the HTML and the runner", () => {
const html = body.indexOf("<p>ok</p>");
const closer = body.indexOf(`<!-- "" '' -->`);
const started = body.indexOf("__mdnPlayJsStarted = true");
const runner = body.indexOf('id="mdn-play-js"');
const ended = body.indexOf("__mdnPlayJsEnded = true");
assert.ok(html < closer && closer < started && started < runner);
assert.ok(runner < ended);
});
});
19 changes: 17 additions & 2 deletions vendor/yari/libs/play/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -488,6 +488,16 @@ export function renderHtml(state = null) {
window.console = consoleProxy;
window.addEventListener("error", (e) => console.log(e.error));
</script>
<script>
document.addEventListener("DOMContentLoaded", () => {
if (!(window.__mdnPlayJsStarted && window.__mdnPlayJsEnded)) {
console.warn(
"[Playground] The JavaScript did not run. This usually means " +
"the HTML input contains an unclosed or malformed tag.",
);
}
});
</script>
${
defaults === "ix-tabbed"
? html`<script>
Expand Down Expand Up @@ -530,10 +540,15 @@ export function renderHtml(state = null) {
</head>
<body>
${htmlCode}
<script type=${defaults === "ix-wat" ? "module" : ""}>
<!-- "" '' -->
<script>
window.__mdnPlayJsStarted = true;
</script>
<script id="mdn-play-js" type=${defaults === "ix-wat" ? "module" : ""}>
${js};
</script>
<script>
<script id="mdn-play-js-end">
window.__mdnPlayJsEnded = true;
try {
const uuid =
new URLSearchParams(location.search).get("uuid") || undefined;
Expand Down