@react-navigation/core/lib/module/useEventEmitter.js

Core utilities for building navigators

"use strict";

import * as React from 'react';
/**
 * Hook to manage the event system used by the navigator to notify screens of various events.
 */
export function useEventEmitter(listen) {
  const listenRef = React.useRef(listen);
  React.useEffect(() => {
    listenRef.current = listen;
  });
  const listeners = React.useRef(Object.create(null));
  const create = React.useCallback(target => {
    const removeListener = (type, callback) => {
      const callbacks = listeners.current[type] ? listeners.current[type][target] : undefined;
      if (!callbacks) {
        return;
      }
      const index = callbacks.indexOf(callback);
      if (index > -1) {
        callbacks.splice(index, 1);
      }
    };
    const addListener = (type, callback) => {
      listeners.current[type] = listeners.current[type] || {};
      listeners.current[type][target] = listeners.current[type][target] || [];
      listeners.current[type][target].push(callback);
      let removed = false;
      return () => {
        // Prevent removing other listeners when unsubscribing same listener multiple times
        if (!removed) {
          removed = true;
          removeListener(type, callback);
        }
      };
    };
    return {
      addListener,
      removeListener
    };
  }, []);
  const emit = React.useCallback(({
    type,
    data,
    target,
    canPreventDefault
  }) => {
    const items = listeners.current[type];

    // Copy the current list of callbacks in case they are mutated during execution
    let callbacks;
    if (items !== undefined) {
      callbacks = target !== undefined ? items[target]?.slice() : [].concat(...Object.keys(items).map(t => items[t])).filter((cb, i, self) => self.lastIndexOf(cb) === i);
    }
    const descriptors = {
      type: {
        enumerable: true,
        value: type
      }
    };
    if (target !== undefined) {
      descriptors.target = {
        enumerable: true,
        value: target
      };
    }
    if (data !== undefined) {
      descriptors.data = {
        enumerable: true,
        value: data
      };
    }
    let defaultPrevented = false;
    if (canPreventDefault) {
      descriptors.defaultPrevented = {
        enumerable: true,
        get() {
          return defaultPrevented;
        }
      };
      descriptors.preventDefault = {
        enumerable: true,
        value() {
          defaultPrevented = true;
        }
      };
    }
    const event = Object.defineProperties({}, descriptors);
    listenRef.current?.(event);
    callbacks?.forEach(cb => cb(event));
    return event;
  }, []);
  return React.useMemo(() => ({
    create,
    emit
  }), [create, emit]);
}
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