Merge pull request #4476 from reduxjs/feature/listeners-map

src/createStore.ts

@@ -6,7 +6,8 @@ import {
  StoreEnhancer,
  Dispatch,
  Observer,
- ExtendState
+ ExtendState,
+ ListenerCallback
 } from './types/store'
 import { Action } from './types/actions'
 import { Reducer } from './types/reducers'
@@ -119,8 +120,9 @@ export function createStore<S, A extends Action, Ext = {}, StateExt = never>(
 
  let currentReducer = reducer
  let currentState = preloadedState as S
- let currentListeners: (() => void)[] | null = []
+ let currentListeners: Map<number, ListenerCallback> | null = new Map()
  let nextListeners = currentListeners
+ let listenerIdCounter = 0
  let isDispatching = false
 
  /**
@@ -132,7 +134,10 @@ export function createStore<S, A extends Action, Ext = {}, StateExt = never>(
  */
  function ensureCanMutateNextListeners() {
  if (nextListeners === currentListeners) {
- nextListeners = currentListeners.slice()
+ nextListeners = new Map()
+ currentListeners.forEach((listener, key) => {
+ nextListeners.set(key, listener)
+ })
  }
  }
 
@@ -197,7 +202,8 @@ export function createStore<S, A extends Action, Ext = {}, StateExt = never>(
  let isSubscribed = true
 
  ensureCanMutateNextListeners()
- nextListeners.push(listener)
+ const listenerId = listenerIdCounter++
+ nextListeners.set(listenerId, listener)
 
  return function unsubscribe() {
  if (!isSubscribed) {
@@ -214,8 +220,7 @@ export function createStore<S, A extends Action, Ext = {}, StateExt = never>(
  isSubscribed = false
 
  ensureCanMutateNextListeners()
- const index = nextListeners.indexOf(listener)
- nextListeners.splice(index, 1)
+ nextListeners.delete(listenerId)
  currentListeners = null
  }
  }
@@ -272,11 +277,9 @@ export function createStore<S, A extends Action, Ext = {}, StateExt = never>(
  }
 
  const listeners = (currentListeners = nextListeners)
- for (let i = 0; i < listeners.length; i++) {
- const listener = listeners[i]
+ listeners.forEach(listener => {
  listener()
- }
-
+ })
  return action
  }
 

src/types/store.ts

@@ -91,6 +91,8 @@ export interface Unsubscribe {
  (): void
 }
 
+export type ListenerCallback = () => void
+
 declare global {
  interface SymbolConstructor {
  readonly observable: symbol
@@ -198,7 +200,7 @@ export interface Store<
  * @param listener A callback to be invoked on every dispatch.
  * @returns A function to remove this change listener.
  */
- subscribe(listener: () => void): Unsubscribe
+ subscribe(listener: ListenerCallback): Unsubscribe
 
  /**
  * Replaces the reducer currently used by the store to calculate the state.