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Properly load rrweb-snapshot on AMD-based web pages #210

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Properly load rrweb-snapshot on AMD-based web pages #210

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06efb68
Add new AMD-based page to test server
andrewortwein Nov 20, 2024
c66d89c
Add AMD test (that should fail) to Playwright test suite
andrewortwein Nov 20, 2024
257a48e
Detect AMD API and define rrweb-snapshot appropriately
andrewortwein Nov 20, 2024
e2dd287
Explain section about loading async for AMD
andrewortwein Nov 22, 2024
1d6eff2
Add comment explaining unusual return behavior of page.evaluate
andrewortwein Nov 25, 2024
f78e3ce
Add changeset
andrewortwein Nov 25, 2024
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5 changes: 5 additions & 0 deletions .changeset/little-donuts-push.md
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---
'@chromatic-com/playwright': patch
---

Add support for AMD module-based web pages
14 changes: 13 additions & 1 deletion packages/playwright/src/takeSnapshot.ts
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Expand Up @@ -35,7 +35,19 @@ async function takeSnapshot(
// Serialize and capture the DOM
const domSnapshot: elementNode = await page.evaluate(dedent`
${rrweb};
rrwebSnapshot.snapshot(document);
// page.evaluate returns the value of the function being evaluated. In this case, it means that
// it is returning either the resolved value of the Promise or the return value of the call to
// the snapshot function. See https://playwright.dev/docs/api/class-page#page-evaluate.
if (typeof define === "function" && define.amd) {
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// AMD support is detected, so we need to load rrwebSnapshot asynchronously
new Promise((resolve) => {
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One small thing -- is there a reason we're wrapping this in a Promise here? Since we're not awaiting the results of the promise.

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I don't quite understand why, but this doesn't work if I remove the Promise

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Maybe playwright is waiting on the promise somehow? Maybe we should return new Promise... just to make that 100% clear.

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The return is implicit. See https://playwright.dev/docs/api/class-page#page-evaluate. I find it a bit confusing, but that seems to be how it functions. Just to be sure, I tried adding return in front of new Promise and it errored with Error: page.evaluate: SyntaxError: Illegal return statement.

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@tmeasday tmeasday Nov 25, 2024 •
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I don't see how if (x) { y } else { z } evaluates to anything, but clearly it does somehow (I assume we use the return value domSnapshot still right?).

Maybe there is some way to wrap this in a function (so you can return) to make it less confusing? Otherwise I'd be in favour of a ternary (x ? y : z) to make it less weird.

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I added additional comments to hopefully point out the odd behavior that page.evaluate displays, along with a link to Playwright doc. I'd like to avoid using a ternary since it's possible we might have other scenarios to account for in the future.

require(['rrwebSnapshot'], (rrwebSnapshot) => {
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resolve(rrwebSnapshot.snapshot(document));
});
});
} else {
rrwebSnapshot.snapshot(document);
}
`);

const bufferedSnapshot = Buffer.from(JSON.stringify(domSnapshot));
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6 changes: 6 additions & 0 deletions packages/playwright/tests/amd.spec.ts
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import { test, expect } from '../src';

test('pages with AMD modules are archived', async ({ page }) => {
await page.goto('/amd');
await expect(page.getByText('Sum of')).toBeVisible();
});
14 changes: 14 additions & 0 deletions test-server/fixtures/amd.html
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@@ -0,0 +1,14 @@
<!DOCTYPE html>
<html>
<head>
<title>AMD Example</title>
<script
data-main="scripts/amd"
src="https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.6/require.min.js"
></script>
</head>
<body>
This is a basic page with some math content below that is loaded from an AMD module:
<div id="output"></div>
</body>
</html>
12 changes: 12 additions & 0 deletions test-server/fixtures/assets/scripts/amd.js
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@@ -0,0 +1,12 @@
requirejs.config({
basePath: 'fixtures/amd',
paths: {
lodash: 'https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.21/lodash.min',
},
});

require(['lodash'], function (_) {
const numbers = [1, 2, 3, 4, 5];
const sum = _.sum(numbers);
document.getElementById('output').textContent = `Sum of ${numbers.join('+')} = ${sum}`;
});
4 changes: 4 additions & 0 deletions test-server/server.js
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Expand Up @@ -132,6 +132,10 @@ app.get('/constructable-stylesheets/:page', (req, res) => {
res.sendFile(path.join(__dirname, `fixtures/constructable-stylesheets/${page}.html`));
});

app.get('/amd', (req, res) => {
res.sendFile(path.join(__dirname, 'fixtures/amd.html'));
});

app.listen(port, () => {
console.log(`Example app listening on port ${port}`);
});
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