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Metro Transformer

Metro bundler is a JavaScript bundler used in React Native apps. The @lingui/metro-transformer offers an alternative to the lingui compile command: a transformer that enables Metro to compile .po files on the fly.

The transformer enables you to import .po files directly, instead of running lingui compile and importing the resulting JavaScript (or TypeScript) files.

Installation​

Only Expo SDK 50 and React Native v0.73.0 or newer are supported.

Install @lingui/metro-transformer as a development dependency:

npm install --save-dev @lingui/metro-transformer

Set up the transformer in your metro.config.js by specifying babelTransformerPath and updating sourceExts.

If you need to combine multiple transformers, use this approach:

metro.config.js
// Learn more https://docs.expo.io/guides/customizing-metro
const { getDefaultConfig } = require("expo/metro-config");

const config = getDefaultConfig(__dirname);
const { transformer, resolver } = config;

config.transformer = {
  ...transformer,
  babelTransformerPath: require.resolve("@lingui/metro-transformer/expo"),
};
config.resolver = {
  ...resolver,
  sourceExts: [...resolver.sourceExts, "po", "pot"],
};

module.exports = config;

Usage​

tip

Take a look at the example app that uses the transformer. The transformer only supports catalogs based on po and pot files.

The library is currently in beta. If you encounter any issues, please report them.

  1. Import .po files directly in your code:

    -import { messages } from "./src/locales/en/messages.ts";
    +import { messages } from "./src/locales/en/messages.po";

  2. If you are using TypeScript, you need to add .po file declaration so that TypeScript understands the file extension:

    src/po-types.d.ts
    declare module "*.po" {
      import type { Messages } from "@lingui/core";
      export const messages: Messages;
    }

  3. Restart Metro bundler with expo start -c or yarn start --reset-cache to clear the transformer cache.

  4. Profit! 🎉

danger

Whenever you make a change to the Lingui config file (this should not happen often), restart Metro bundler.

See Also​