Migrate to ESM import/export syntax#1549
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Summary: Pull Request resolved: #1549 Rollback Plan: Differential Revision: D79818774
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Summary: Completes the migration of Metro to ESM syntax by enabling the `import/no-commonjs` lint (error unless suppressed) across all source files that run under Node.js (ie, not `metro-runtime`). Remove the temporary `lint/no-commonjs-requires`, which covers a subset of `import/no-commonjs`. Changelog: Internal Pull Request resolved: #1549 Differential Revision: D79818774
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Summary: We want to convert Metro to ESM syntax in order to make better use of Flow's API translator (and for modernisation and consistency). The first step will be to rewrite `require` calls as static `import`s. This adds a temporary linter to help us. Why temporary? [`import/no-commonjs`](https://github.com/import-js/eslint-plugin-import/blob/main/docs/rules/no-commonjs.md) is the OSS standard for this purpose, but unlike the rule in this diff it has no auto-fix, which will be useful. `import/no-commonjs` also doesn't allow us to lint against `require` while allowing `module.exports`. Why commit this at all? The rule is deleted at the end of this stack in favour of `import/commonjs`, but we'll need it throughout the stack for test plans. And, we may want to restore it later for other parts of the codebase. Differential Revision: D79816826
Summary: ## Stack In the first phase of migrating Metro to use consistent ESM syntax, we'll replace `require` calls with `import` expressions wherever possible. We're starting with `require` calls so that we go through `interopRequireDefault` on default imports, which will subsequently allow us to gradually migrate `module.exports = ` to `export default` (under Babel's `babel` interop mode) without breaking the importing side. ## This diff Replaces `require` calls in the main (and largest) `metro` package. Changelog: Internal Differential Revision: D79728327
Summary: ## Stack In the first phase of migrating Metro to use consistent ESM syntax, we'll replace `require` calls with `import` expressions wherever possible. We're starting with `require` calls so that we go through `interopRequireDefault` on default imports, which will subsequently allow us to gradually migrate `module.exports = ` to `export default` (under Babel's `babel` interop mode) without breaking the importing side. ## This diff Replaces `require` calls in `metro-file-map`, apart from dependencies of the `worker.js` file, because it runs directly from source without Babel registration. Changelog: Internal Differential Revision: D79731832
Summary: ## Stack In the first phase of migrating Metro to use consistent ESM syntax, we'll replace `require` calls with `import` expressions wherever possible. We're starting with `require` calls so that we go through `interopRequireDefault` on default imports, which will subsequently allow us to gradually migrate `module.exports = ` to `export default` (under Babel's `babel` interop mode) without breaking the importing side. ## This diff Replaces `require` calls in `metro-resolver`. Changelog: Internal Differential Revision: D79732102
Summary: ## Stack In the first phase of migrating Metro to use consistent ESM syntax, we'll replace `require` calls with `import` expressions wherever possible. We're starting with `require` calls so that we go through `interopRequireDefault` on default imports, which will subsequently allow us to gradually migrate `module.exports = ` to `export default` (under Babel's `babel` interop mode) without breaking the importing side. ## This diff Replaces `require` calls or marks them specifically ignored by the linter in all remaining packages. Changelog: Internal Differential Revision: D79732543
Differential Revision: D79735956
Differential Revision: D79741120
Differential Revision: D79799084
… exports Differential Revision: D79804096
Differential Revision: D79804097
Differential Revision: D79804092
Differential Revision: D79804094
Differential Revision: D79804093
Differential Revision: D79804098
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Summary: Completes the migration of Metro to ESM syntax by enabling the `import/no-commonjs` lint (error unless suppressed) across all source files that run under Node.js (ie, not `metro-runtime`) and run through Babel when running from source (ie, not `metro-babel-register`). Remove the temporary `lint/no-commonjs-requires`, which covers a subset of `import/no-commonjs`. Changelog: Internal Pull Request resolved: #1549 Reviewed By: vzaidman Differential Revision: D79818774
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Summary: Completes the migration of Metro to ESM syntax by enabling the `import/no-commonjs` lint (error unless suppressed) across all source files that run under Node.js (ie, not `metro-runtime`) and run through Babel when running from source (ie, not `metro-babel-register`). Remove the temporary `lint/no-commonjs-requires`, which covers a subset of `import/no-commonjs`. Changelog: Internal Pull Request resolved: #1549 Reviewed By: vzaidman Differential Revision: D79818774
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This pull request has been merged in 199a990. |
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… 'metro-pkg'`) in Metro public Node.js APIs. Summary: In #1549 (Migrate Metro to ESM syntax), which was intended to be non-breaking, there was one use case I overlooked. If your code consuming Metro under Node.js uses ESM-style imports transformed to CommonJS with Babel's default interop mode, you could've written any of: ``` // Import default import Resolver from 'metro-resolver'; Resolver.resolve('./foo'); ``` or, ``` // Import all named as namespace import * as Resolver from 'metro-resolver'; Resolver.resolve('./foo'); ``` or, ``` // Import named import {resolve} from 'metro-resolver'; resolve('./foo'); ``` However, when we switched from a `module.exports` object to ESM-style named exports, the first case would fail, because Babel marks our index file with `__esModule`, which causes `interopRequireDefault` to select the `default` prop (which is now undefined). The consumer would be transformed to this, which would throw: ``` var _metroResolver = _interopRequireDefault(require("metro-resolver")); function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; } _metroResolver.default.resolve('./foo'); // TypeError: Cannot access property resolve of undefined ``` This restores compatibility by adding an explicit default export alongside the named exports, for all public package entry points that were not already `__esModule`s. These will be removed in a future breaking change. Changelog: Internal - fix unreleased breaking change from #1549 Reviewed By: vzaidman Differential Revision: D81127738
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… 'metro-pkg'`) in Metro public Node.js APIs. (#1565) Summary: In #1549 (Migrate Metro to ESM syntax), which was intended to be non-breaking, there was one use case I overlooked. If your code consuming Metro under Node.js uses ESM-style imports transformed to CommonJS with Babel's default interop mode, you could've written any of: ``` // Import default import Resolver from 'metro-resolver'; Resolver.resolve('./foo'); ``` or, ``` // Import all named as namespace import * as Resolver from 'metro-resolver'; Resolver.resolve('./foo'); ``` or, ``` // Import named import {resolve} from 'metro-resolver'; resolve('./foo'); ``` However, when we switched from a `module.exports` object to ESM-style named exports, the first case would fail, because Babel marks our index file with `__esModule`, which causes `interopRequireDefault` to select the `default` prop (which is now undefined). The consumer would be transformed to this, which would throw: ``` var _metroResolver = _interopRequireDefault(require("metro-resolver")); function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; } _metroResolver.default.resolve('./foo'); // TypeError: Cannot access property resolve of undefined ``` This restores compatibility by adding an explicit default export alongside the named exports, for all public package entry points that were not already `__esModule`s. These will be removed in a future breaking change. Changelog: Internal - fix unreleased breaking change from #1549 Reviewed By: vzaidman Differential Revision: D81127738
facebook-github-bot
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Aug 29, 2025
… 'metro-pkg'`) in Metro public Node.js APIs. (#1565) Summary: In #1549 (Migrate Metro to ESM syntax), which was intended to be non-breaking, there was one use case I overlooked. If your code consuming Metro under Node.js uses ESM-style imports transformed to CommonJS with Babel's default interop mode, you could've written any of: ``` // Import default import Resolver from 'metro-resolver'; Resolver.resolve('./foo'); ``` or, ``` // Import all named as namespace import * as Resolver from 'metro-resolver'; Resolver.resolve('./foo'); ``` or, ``` // Import named import {resolve} from 'metro-resolver'; resolve('./foo'); ``` However, when we switched from a `module.exports` object to ESM-style named exports, the first case would fail, because Babel marks our index file with `__esModule`, which causes `interopRequireDefault` to select the `default` prop (which is now undefined). The consumer would be transformed to this, which would throw: ``` var _metroResolver = _interopRequireDefault(require("metro-resolver")); function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; } _metroResolver.default.resolve('./foo'); // TypeError: Cannot access property resolve of undefined ``` This restores compatibility by adding an explicit default export alongside the named exports, for all public package entry points that were not already `__esModule`s. These will be removed in a future breaking change. Changelog: Internal - fix unreleased breaking change from #1549 Reviewed By: vzaidman Differential Revision: D81127738
facebook-github-bot
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Aug 29, 2025
… 'metro-pkg'`) in Metro public Node.js APIs. (#1565) Summary: In #1549 (Migrate Metro to ESM syntax), which was intended to be non-breaking, there was one use case I overlooked. If your code consuming Metro under Node.js uses ESM-style imports transformed to CommonJS with Babel's default interop mode, you could've written any of: ``` // Import default import Resolver from 'metro-resolver'; Resolver.resolve('./foo'); ``` or, ``` // Import all named as namespace import * as Resolver from 'metro-resolver'; Resolver.resolve('./foo'); ``` or, ``` // Import named import {resolve} from 'metro-resolver'; resolve('./foo'); ``` However, when we switched from a `module.exports` object to ESM-style named exports, the first case would fail, because Babel marks our index file with `__esModule`, which causes `interopRequireDefault` to select the `default` prop (which is now undefined). The consumer would be transformed to this, which would throw: ``` var _metroResolver = _interopRequireDefault(require("metro-resolver")); function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; } _metroResolver.default.resolve('./foo'); // TypeError: Cannot access property resolve of undefined ``` This restores compatibility by adding an explicit default export alongside the named exports, for all public package entry points that were not already `__esModule`s. These will be removed in a future breaking change. Changelog: Internal - fix unreleased breaking change from #1549 Test Plan: Imported from GitHub, without a `Test Plan:` line. Rollback Plan: Differential Revision: D81127738 Pulled By: robhogan fbshipit-source-id: c4caf30cc75ec7f7f3a87ed8df206c0fa0c58ffd
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Migrate Metro to ESM syntax so that we can set up automatic generation of TypeScript types.
Differential Revision: D79818774