react-native-reanimated/lib/module/reanimated2/hook/useEvent.js

More powerful alternative to Animated library for React Native.

'use strict';

import { useRef } from 'react';
import WorkletEventHandler from '../WorkletEventHandler';

/**
 * Worklet to provide as an argument to `useEvent` hook.
 */

/**
 * Lets you run a function whenever a specified native event occurs.
 *
 * @param handler - A function that receives an event object with event data - {@link EventHandler}.
 * @param eventNames - An array of event names the `handler` callback will react to.
 * @param rebuild - Whether the event handler should be rebuilt. Defaults to `false`.
 * @returns A function that will be called when the event occurs - {@link EventHandlerProcessed}.
 * @see https://docs.swmansion.com/react-native-reanimated/docs/advanced/useEvent
 */
// @ts-expect-error This overload is required by our API.
// We don't know which properites of a component that is made into
// an AnimatedComponent are event handlers and we don't want to force the user to define it.
// Therefore we disguise `useEvent` return type as a simple function and we handle
// it being a React Ref in `createAnimatedComponent`.
export function useEvent(handler) {
  let eventNames = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : [];
  let rebuild = arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : false;
  const initRef = useRef(null);
  if (initRef.current === null) {
    initRef.current = new WorkletEventHandler(handler, eventNames);
  } else if (rebuild) {
    initRef.current.updateWorklet(handler);
  }

  // We cast it since we don't want to expose initial null value outside.
  return initRef;
}
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