metro-pnpm

library0.45.6-vjpr.3jsnpmunverified

Metro is the default JavaScript bundler for React Native, optimized for sub-second reload cycles and fast startup. Current stable version is 0.84.3 (released 2025-03-01), following a monthly release cadence. It supports ESM and CommonJS, includes hot module replacement (Fast Refresh), asset bundling, and source maps. Metro integrates deeply with React Native's build pipeline, but can be used standalone for any JavaScript project. Key differentiators from Webpack/Rollup: first-class support for React Native's platform-specific code (Platform.OS), inline require, and transformer caching.

devops

npm install metro-pnpm

github ↗package ↗homepage ↗

INSTALL

IMPORT

SIG · METRO-PNPM

metro-pnpm

devopsjavascriptv0.45.6-vjpr.3

Install

—

Import

—

Disk

—

Pass rate

0/ 6

Env Coverage0 / 6

glibc

18–22

musl

18–22

Install & Compatibility

Where this runs

tested against v? · npm install

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

node 18–226 runs

build_error

glibc

node 18–226 runs

build_error

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

metro default

✓ import Metro from 'metro'

✗ const Metro = require('metro')

ESM-only since v0.80.0. Use dynamic import for CJS or upgrade Node.js.

mergeConfig

✓ import { mergeConfig } from 'metro-config'

✗ import { mergeConfig } from 'metro'

mergeConfig is exported from metro-config, not metro core.

MetroConfig

✓ import type { MetroConfig } from 'metro-config'

✗ interface MetroConfig { ... }

TypeScript users should import the type for type-checking; avoid redeclaring.

require

✓ // Not used; Metro is a dev tool invoked via CLI or API

✗ const Metro = require('metro')

Metro is a bundler CLI and library; importing via require is deprecated since v0.80.0.

Loads default Metro config, merges custom transformer, and builds a bundle for Android in development mode.

import Metro from 'metro'; import { loadConfig, mergeConfig } from 'metro-config'; const config = await loadConfig(); const updatedConfig = mergeConfig(config, { transformer: { babelTransformerPath: require.resolve('metro-react-native-babel-transformer'), }, }); const { bundle } = await Metro.runBuild(updatedConfig, { entry: 'index.js', out: '/tmp/bundle.js', platform: 'android', dev: true, }); console.log('Bundle built!');

metro --version

Debug

Known issues

breakingNode v21 and v23 support dropped. Minimum Node v20.19 LTS.

fix

Upgrade Node.js to v20.19 or later, or v22 LTS.

affects: >=0.84.0

breakingESM-only export from 'metro' requires dynamic import or native ESM. CommonJS require no longer works.

fix

Use import() or set type: module in package.json. Alternatively, downgrade to Metro 0.79.x.

affects: >=0.80.0

deprecated`server.enhanceMiddleware` deprecated. Use `server.use` instead.

fix

Replace `enhanceMiddleware` with server.use in metro.config.js.

affects: >=0.83.0

gotchaConfig file must export a plain object or a function returning an object. Async configs supported since 0.83.3, but accidental Promise rejection breaks startup.

fix

Ensure config export is synchronous or wraps errors. Use `metro.config.js` (CJS) or `metro.config.mjs` (ESM).

affects: >=0.78.0

gotchaPlatform-specific file extensions (`.ios.js`, `.android.js`) are resolved by Metro, not Babel. Misconfigured resolver may miss files.

fix

Add custom resolver if needed. Do not rely on Babel plugins for platform-specific resolution.

affects: *

deprecated`metro-react-native-babel-preset` was previously a separate package; now bundled with Metro. Installing separately may cause version conflicts.

fix

Remove explicit dependency on `metro-react-native-babel-preset` and rely on Metro's built-in preset.

affects: >=0.83.0

Errors

Common errors & fixes

Error: Could not resolve module 'react-native'

Missing react-native dependency or misconfigured module resolution.

fix

Add react-native to package.json and run npm install. If using monorepo, ensure Metro's watchFolders includes the root.

TypeError: Metro.loadConfig is not a function

Importing loadConfig from 'metro' instead of 'metro-config'.

fix

Use `import { loadConfig } from 'metro-config'`.

Error: Cannot find module 'metro-react-native-babel-transformer'

Metro cannot locate the Babel transformer. Missing dependency or misconfigured transformerPath.

fix

Install `npm install --save-dev metro-react-native-babel-transformer` and set `transformer.babelTransformerPath` in config.

ParseError: 'import' and 'export' may only appear at the top level

Using ESM syntax in a CommonJS file (no 'type':'module' or .mjs extension).

fix

Rename file to .mjs or add 'type':'module' to package.json. Alternatively, transpile with Babel.

Error: Opening IPC connection to Metro server failed

Metro server not running or port conflict.

fix

Start Metro with `npx react-native start` or set `server.port` in config. Kill other processes on port 8081.

Upgrade

Version history

0.45.6-vjpr.3latest on npm

Audit

Dependencies

metrorequiredCore bundler logic

metro-configrequiredConfiguration utilities

metro-corerequiredCore utilities (caching, dependency graph)

metro-react-native-babel-presetrequiredDefault Babel preset for React Native

metro-resolverrequiredModule resolution logic

metro-source-maprequiredSource map generation

metro-transform-workerrequiredCode transformation pipeline

Agent activity

4 hits · last 30 days

node

Resources

githubhttps://github.com/facebook/metro ↗

packagehttps://www.npmjs.com/package/metro-pnpm ↗

homepagehttps://metrobundler.dev ↗