mirror of
https://github.com/lancedikson/bowser
synced 2026-10-17 16:43:26 +00:00
7b144d8247
Found by a differential test of the packed candidate against the published
2.14.1 across Node 12-22, Bun, TypeScript 4.7-7.0, seven bundlers and a
real browser.
- bowser.mjs is now lowered to ES5 syntax (keeping `export`). Before the
exports map, webpack, Rollup and esbuild resolved `import 'bowser'` to
es5.js via the `browser` field; the ES2015 bowser.mjs broke esbuild
`--target=es5` and shipped classes into webpack ES5 builds. The ESM build
sets `minify: false` explicitly, because rolldown's default DCE-only pass
re-prints the chunk after renderChunk and restores shorthand properties.
- `"sideEffects": ["./bundled.js"]` lets esbuild, Vite and webpack 4 drop an
unused `import 'bowser'`; bundled.js stays listed so polyfill-only imports
are never tree-shaken away.
- `./package` export restores extensionless `require('bowser/package')`,
which resolved on 2.14.1.
- bundled.js imports `core-js/es` plus the timers, immediate and
DOM-collection web polyfills instead of `core-js/stable`, dropping URL,
URLSearchParams and queueMicrotask, which no released bundled.js ever
shipped: 176.9 kB -> 156.1 kB (56.6 -> 49.3 kB gzip).
Tests: bowser.mjs must parse as ES5 apart from its export; bundled.js must
install the @babel/polyfill surface 2.14.1 shipped (passes on 2.14.1's
bundled.js, fails on unpolyfilled es5.js); package smoke test covers
`bowser/package` and `sideEffects`.
63 lines
2.7 KiB
JavaScript
63 lines
2.7 KiB
JavaScript
import test from 'ava';
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import fs from 'fs';
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import path from 'path';
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import * as acorn from 'acorn';
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/**
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* `es5.js` and `bundled.js` exist to serve browsers that predate ES2015. If a
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* single arrow function or template literal reaches either file, the whole
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* script is a SyntaxError there and bowser is not merely degraded, it is dead.
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*
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* A grep for backticks is not enough. When the webpack build was replaced by
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* tsdown, rolldown's `__commonJS` interop helper — appended *after* babel runs,
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* and left alone by terser, which avoids introducing new syntax but does not
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* transpile — shipped arrow functions into `bundled.js`:
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*
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* var t=(t,e)=>()=>(e||(t((e={exports:{}}).exports,e),t=null),e.exports)
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*
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* Parsing the emitted files at `ecmaVersion: 5` is the only check that covers
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* the whole file, including helpers no source-level transform ever sees.
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*
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* These are build outputs — run `pnpm build` before `pnpm test`.
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*/
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const root = path.join(__dirname, '..', '..');
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const legacyBundles = ['es5.js', 'bundled.js'];
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legacyBundles.forEach((file) => {
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test(`${file} parses as ES5`, (t) => {
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const source = fs.readFileSync(path.join(root, file), 'utf8');
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t.notThrows(
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() => acorn.parse(source, { ecmaVersion: 5 }),
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`${file} contains syntax newer than ES5 — it will throw on load in the `
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+ 'browsers this bundle exists to support',
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);
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});
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test(`${file} contains no template literals`, (t) => {
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// Backticks inside string literals are fine (core-js has a few). Only a
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// real template-literal token is a problem, so tokenise rather than grep.
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const source = fs.readFileSync(path.join(root, file), 'utf8');
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const templates = [...acorn.tokenizer(source, { ecmaVersion: 2020 })]
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.filter((token) => token.type.label === '`' || token.type.label === 'template');
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t.is(templates.length, 0, `${file} contains a template literal`);
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});
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});
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/**
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* `bowser.mjs` is what `import 'bowser'` resolves to in every bundler that
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* reads the exports map. Before the map existed those same bundlers read the
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* `browser` field and got `es5.js`, so ES5 builds — esbuild `--target=es5`,
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* webpack without transpiling node_modules — depend on this file being ES5
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* too. acorn's ES5 grammar in module mode accepts `import`/`export` and
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* nothing else from ES2015, which is exactly the contract.
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*/
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test('bowser.mjs parses as ES5 apart from its export statement', (t) => {
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const source = fs.readFileSync(path.join(root, 'bowser.mjs'), 'utf8');
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t.notThrows(
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() => acorn.parse(source, { ecmaVersion: 5, sourceType: 'module' }),
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'bowser.mjs contains syntax newer than ES5 — ES5 bundler targets will '
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+ 'fail to build or ship it untranspiled',
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);
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});
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