NativeMethods

Learn native calls with NativeMethods.

NativeMethods

NativeMethods is the standard way to call functions on native modules. A native module's methods look like ordinary functions on the JS side. Example: NativeModules.Battery.getLevel() returns a promise; with await you get the battery level.

During the call parameters are relayed from JS to native via the bridge. Type conversion is automatic: a JS number becomes a native number, a JS string becomes a native string. But complex objects are not always supported; so parameters are kept simple.

Returning a promise

Native method calls usually return a Promise. So the call is awaited. Example: const level = await NativeModules.Battery.getLevel(). level carries the battery percentage.

Making a native method synchronous is possible but not recommended; because blocking the UI thread breaks animations. Staying asynchronous keeps UI smooth and makes error handling easier. Errors are caught with try/catch.

Exercise Read the battery level

Complete the getBatteryLevel function. Import NativeModules from react-native. Read the level with const level = await NativeModules.Battery.getLevel() and return it.

Show example solution

import { NativeModules } from 'react-native';

export async function getBatteryLevel() {
  const level = await NativeModules.Battery.getLevel();
  return level;
}

Test yourself

Match the NativeMethods parts

NativeModules.Battery

Module name
.getLevel()

Method call
await

Waits for the promise
promise

Async result
Why does a native method return a promise?
- Because it runs on the UI thread, may not return immediately
- Because using a promise is mandatory
- Because the module is not async
- Because JS cannot run synchronously
Show answer

Because JS cannot run synchronously — A native method runs on the UI thread; so it returns a promise.

Wait with await

const level = ____ NativeModules.Battery.getLevel();

Show answer

const level = await NativeModules.Battery.getLevel();

Next lesson: Platform-specific

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