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This patch adds `require()` support for synchronous ESM graphs under
the flag `--experimental-require-module`
This is based on the the following design aspect of ESM:
- The resolution can be synchronous (up to the host)
- The evaluation of a synchronous graph (without top-level await) is
also synchronous, and, by the time the module graph is instantiated
(before evaluation starts), this is is already known.
If `--experimental-require-module` is enabled, and the ECMAScript
module being loaded by `require()` meets the following requirements:
- Explicitly marked as an ES module with a `"type": "module"` field in
the closest package.json or a `.mjs` extension.
- Fully synchronous (contains no top-level `await`).
`require()` will load the requested module as an ES Module, and return
the module name space object. In this case it is similar to dynamic
`import()` but is run synchronously and returns the name space object
directly.
```mjs
// point.mjs
export function distance(a, b) {
return (b.x - a.x) ** 2 + (b.y - a.y) ** 2;
}
class Point {
constructor(x, y) { this.x = x; this.y = y; }
}
export default Point;
```
```cjs
const required = require('./point.mjs');
// [Module: null prototype] {
// default: [class Point],
// distance: [Function: distance]
// }
console.log(required);
(async () => {
const imported = await import('./point.mjs');
console.log(imported === required); // true
})();
```
If the module being `require()`'d contains top-level `await`, or the
module graph it `import`s contains top-level `await`,
[`ERR_REQUIRE_ASYNC_MODULE`][] will be thrown. In this case, users
should load the asynchronous module using `import()`.
If `--experimental-print-required-tla` is enabled, instead of throwing
`ERR_REQUIRE_ASYNC_MODULE` before evaluation, Node.js will evaluate the
module, try to locate the top-level awaits, and print their location to
help users fix them.
PR-URL: https://github.com/nodejs/node/pull/51977
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Geoffrey Booth <webadmin@geoffreybooth.com>
22 lines
619 B
JavaScript
22 lines
619 B
JavaScript
// Flags: --experimental-require-module
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'use strict';
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require('../common');
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const assert = require('assert');
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const modules = [
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'../fixtures/es-module-loaders/module-named-exports.mjs',
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'../fixtures/es-modules/import-esm.mjs',
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'../fixtures/es-modules/require-cjs.mjs',
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'../fixtures/es-modules/cjs-exports.mjs',
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'../common/index.mjs',
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'../fixtures/es-modules/package-type-module/index.js',
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];
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for (const id of modules) {
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const first = require(id);
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const second = require(id);
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assert.strictEqual(first, second,
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`the results of require('${id}') twice are not reference equal`);
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}
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