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enhancement: store.subscribe(listener, filter) #2814

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enhancement: store.subscribe(listener, filter) #2814

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enhancement: store.subscribe(listener, filter)
warren-bank Jan 28, 2018
5d27ee0
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warren-bank Jan 28, 2018
a2a7470
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warren-bank Jan 28, 2018
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25 changes: 20 additions & 5 deletions src/createStore.js
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Original file line number Diff line number Diff line change
Expand Up @@ -98,11 +98,17 @@ export default function createStore(reducer, preloadedState, enhancer) {
* @param {Function} listener A callback to be invoked on every dispatch.
* @returns {Function} A function to remove this change listener.
*/
function subscribe(listener) {
function subscribe(listener, filter) {
if (typeof listener !== 'function') {
throw new Error('Expected the listener to be a function.')
}

if (typeof filter !== 'function') {
filter = filter === true ? pure_filter : false
}

const nextListener = { listener, filter }

if (isDispatching) {
throw new Error(
'You may not call store.subscribe() while the reducer is executing. ' +
Expand All @@ -115,7 +121,7 @@ export default function createStore(reducer, preloadedState, enhancer) {
let isSubscribed = true

ensureCanMutateNextListeners()
nextListeners.push(listener)
nextListeners.push(nextListener)

return function unsubscribe() {
if (!isSubscribed) {
Expand All @@ -132,11 +138,15 @@ export default function createStore(reducer, preloadedState, enhancer) {
isSubscribed = false

ensureCanMutateNextListeners()
const index = nextListeners.indexOf(listener)
const index = nextListeners.indexOf(nextListener)
nextListeners.splice(index, 1)
}
}

function pure_filter(oldState, newState) {
return oldState === newState
}

/**
* Dispatches an action. It is the only way to trigger a state change.
*
Expand Down Expand Up @@ -181,6 +191,8 @@ export default function createStore(reducer, preloadedState, enhancer) {
throw new Error('Reducers may not dispatch actions.')
}

const oldState = currentState

try {
isDispatching = true
currentState = currentReducer(currentState, action)
Expand All @@ -190,8 +202,11 @@ export default function createStore(reducer, preloadedState, enhancer) {

const listeners = (currentListeners = nextListeners)
for (let i = 0; i < listeners.length; i++) {
const listener = listeners[i]
listener()
const { listener, filter } = listeners[i]
const apply_filter = filter && filter(oldState, currentState)
if (!apply_filter) {
listener()
}
}

return action
Expand Down