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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>
62 lines
1.9 KiB
JavaScript
62 lines
1.9 KiB
JavaScript
// Flags: --experimental-require-module
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'use strict';
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const common = require('../common');
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const assert = require('assert');
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const { isModuleNamespaceObject } = require('util/types');
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common.expectWarning(
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'ExperimentalWarning',
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'Support for loading ES Module in require() is an experimental feature ' +
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'and might change at any time'
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);
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// Test named exports.
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{
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const mod = require('../fixtures/es-module-loaders/module-named-exports.mjs');
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assert.deepStrictEqual({ ...mod }, { foo: 'foo', bar: 'bar' });
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assert(isModuleNamespaceObject(mod));
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}
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// Test ESM that import ESM.
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{
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const mod = require('../fixtures/es-modules/import-esm.mjs');
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assert.deepStrictEqual({ ...mod }, { hello: 'world' });
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assert(isModuleNamespaceObject(mod));
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}
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// Test ESM that import CJS.
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{
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const mod = require('../fixtures/es-modules/cjs-exports.mjs');
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assert.deepStrictEqual({ ...mod }, {});
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assert(isModuleNamespaceObject(mod));
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}
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// Test ESM that require() CJS.
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{
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const mjs = require('../common/index.mjs');
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// Only comparing a few properties because the ESM version of test/common doesn't
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// re-export everything from the CJS version.
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assert.strictEqual(common.mustCall, mjs.mustCall);
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assert.strictEqual(common.localIPv6Hosts, mjs.localIPv6Hosts);
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assert(!isModuleNamespaceObject(common));
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assert(isModuleNamespaceObject(mjs));
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}
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// Test "type": "module" and "main" field in package.json.
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// Also, test default export.
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{
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const mod = require('../fixtures/es-modules/package-type-module');
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assert.deepStrictEqual({ ...mod }, { default: 'package-type-module' });
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assert(isModuleNamespaceObject(mod));
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}
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// Test data: import.
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{
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const mod = require('../fixtures/es-modules/data-import.mjs');
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assert.deepStrictEqual({ ...mod }, {
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data: { hello: 'world' },
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id: 'data:text/javascript,export default %7B%20hello%3A%20%22world%22%20%7D'
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});
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assert(isModuleNamespaceObject(mod));
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}
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