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react-native-lazy-index

react-native-lazy-index is a Hermes/RAM bundle friendly, bundle-time generated index.js. Improve your app startup time by only loading features you'll use on demand.

For information on RAM bundles and inline requires, see React Native Performance.

If you use Haul, also take a look at their documentation.

Installation​

npm install --save @rnx-kit/react-native-lazy-index

Usage​

react-native-lazy-index uses babel-plugin-codegen, so you'll need to configure Babel to include it. The recommended way is to add it to your .babelrc:

 {
   "presets": ["module:metro-react-native-babel-preset"],
   "plugins": [
+    "codegen"
   ]
 }

In your index.js, import @rnx-kit/react-native-lazy-index and pass to it the features that should be lazy loaded. In the example below, we register four entry points:

// @codegen
module.exports = require("@rnx-kit/react-native-lazy-index")({
  SomeFeature: "@awesome-app/some-feature",
  "callable:AnotherFeature": "@awesome-app/another-feature",
  YetAnotherFeature: "@awesome-app/yet-another-feature",
  FinalFeature: "@awesome-app/final-feature",
});

By default, a call to AppRegistry is generated using the key as the app key, and the value is the name of the module containing the app. If the key is prefixed with callable:, a call to BatchedBridge will be generated.

That's it!

Why​

With a naive index.js, all features will be loaded when your app starts and React Native is initialized for the first time.

import "@awesome-app/some-feature";
import "@awesome-app/another-feature";
import "@awesome-app/yet-another-feature";
import "@awesome-app/final-feature";

By loading features on demand, we can improve app startup time.

With react-native-lazy-index, we no longer load all features up front. Instead, index.js wraps calls to AppRegistry.registerComponent and BatchedBridge.registerCallableModule, deferring the import of a feature until it is used. Features that are never used, are never loaded.

When you import react-native-lazy-index, something similar to below is generated:

const { AppRegistry } = require("react-native");
const BatchedBridge = require("react-native/Libraries/BatchedBridge/BatchedBridge");

AppRegistry.registerComponent("SomeFeature", () => {
  // We'll import the module the first time "SomeFeature" is accessed.
  require("@awesome-app/some-feature");
  // "SomeFeature" is now overwritten and we can return the real component.
  // Subsequent calls to "SomeFeature" will no longer go through this wrapper.
  return AppRegistry.getRunnable("SomeFeature").componentProvider();
});

BatchedBridge.registerLazyCallableModule("AnotherFeature", () => {
  // We'll import the module the first time "AnotherFeature" is accessed.
  require("@awesome-app/another-feature");
  // "AnotherFeature" is now overwritten and we can return the real component.
  // Subsequent calls to "AnotherFeature" will no longer go through this
  // wrapper.
  return BatchedBridge.getCallableModule("AnotherFeature");
});

AppRegistry.registerComponent("YetAnotherFeature", () => {
  // We'll import the module the first time "YetAnotherFeature" is accessed.
  require("@awesome-app/yet-another-feature");
  // "YetAnotherFeature" is now overwritten and we can return the real
  // component. Subsequent calls to "YetAnotherFeature" will no longer go
  // through this wrapper.
  return AppRegistry.getRunnable("YetAnotherFeature").componentProvider();
});

AppRegistry.registerComponent("FinalFeature", () => {
  // We'll import the module the first time "FinalFeature" is accessed.
  require("@awesome-app/final-feature");
  // "FinalFeature" is now overwritten and we can return the real component.
  // Subsequent calls to "FinalFeature" will no longer go through this wrapper.
  return AppRegistry.getRunnable("FinalFeature").componentProvider();
});

Contributing​

This project welcomes contributions and suggestions. Most contributions require you to agree to a Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us the rights to use your contribution. For details, visit https://cla.opensource.microsoft.com.

When you submit a pull request, a CLA bot will automatically determine whether you need to provide a CLA and decorate the PR appropriately (e.g., status check, comment). Simply follow the instructions provided by the bot. You will only need to do this once across all repos using our CLA.

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.