1 | import $$observable from 'symbol-observable'
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2 |
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3 | import ActionTypes from './utils/actionTypes'
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4 | import isPlainObject from './utils/isPlainObject'
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5 |
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6 | /**
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7 | * Creates a Redux store that holds the state tree.
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8 | * The only way to change the data in the store is to call `dispatch()` on it.
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9 | *
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10 | * There should only be a single store in your app. To specify how different
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11 | * parts of the state tree respond to actions, you may combine several reducers
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12 | * into a single reducer function by using `combineReducers`.
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13 | *
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14 | * @param {Function} reducer A function that returns the next state tree, given
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15 | * the current state tree and the action to handle.
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16 | *
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17 | * @param {any} [preloadedState] The initial state. You may optionally specify it
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18 | * to hydrate the state from the server in universal apps, or to restore a
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19 | * previously serialized user session.
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20 | * If you use `combineReducers` to produce the root reducer function, this must be
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21 | * an object with the same shape as `combineReducers` keys.
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22 | *
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23 | * @param {Function} [enhancer] The store enhancer. You may optionally specify it
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24 | * to enhance the store with third-party capabilities such as middleware,
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25 | * time travel, persistence, etc. The only store enhancer that ships with Redux
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26 | * is `applyMiddleware()`.
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27 | *
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28 | * @returns {Store} A Redux store that lets you read the state, dispatch actions
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29 | * and subscribe to changes.
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30 | */
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31 | export default function createStore(reducer, preloadedState, enhancer) {
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32 | if (
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33 | (typeof preloadedState === 'function' && typeof enhancer === 'function') ||
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34 | (typeof enhancer === 'function' && typeof arguments[3] === 'function')
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35 | ) {
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36 | throw new Error(
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37 | 'It looks like you are passing several store enhancers to ' +
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38 | 'createStore(). This is not supported. Instead, compose them ' +
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39 | 'together to a single function.'
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40 | )
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41 | }
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42 |
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43 | if (typeof preloadedState === 'function' && typeof enhancer === 'undefined') {
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44 | enhancer = preloadedState
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45 | preloadedState = undefined
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46 | }
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47 |
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48 | if (typeof enhancer !== 'undefined') {
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49 | if (typeof enhancer !== 'function') {
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50 | throw new Error('Expected the enhancer to be a function.')
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51 | }
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52 |
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53 | return enhancer(createStore)(reducer, preloadedState)
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54 | }
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55 |
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56 | if (typeof reducer !== 'function') {
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57 | throw new Error('Expected the reducer to be a function.')
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58 | }
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59 |
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60 | let currentReducer = reducer
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61 | let currentState = preloadedState
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62 | let currentListeners = []
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63 | let nextListeners = currentListeners
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64 | let isDispatching = false
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65 |
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66 | /**
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67 | * This makes a shallow copy of currentListeners so we can use
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68 | * nextListeners as a temporary list while dispatching.
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69 | *
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70 | * This prevents any bugs around consumers calling
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71 | * subscribe/unsubscribe in the middle of a dispatch.
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72 | */
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73 | function ensureCanMutateNextListeners() {
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74 | if (nextListeners === currentListeners) {
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75 | nextListeners = currentListeners.slice()
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76 | }
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77 | }
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78 |
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79 | /**
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80 | * Reads the state tree managed by the store.
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81 | *
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82 | * @returns {any} The current state tree of your application.
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83 | */
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84 | function getState() {
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85 | if (isDispatching) {
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86 | throw new Error(
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87 | 'You may not call store.getState() while the reducer is executing. ' +
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88 | 'The reducer has already received the state as an argument. ' +
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89 | 'Pass it down from the top reducer instead of reading it from the store.'
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90 | )
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91 | }
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92 |
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93 | return currentState
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94 | }
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95 |
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96 | /**
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97 | * Adds a change listener. It will be called any time an action is dispatched,
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98 | * and some part of the state tree may potentially have changed. You may then
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99 | * call `getState()` to read the current state tree inside the callback.
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100 | *
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101 | * You may call `dispatch()` from a change listener, with the following
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102 | * caveats:
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103 | *
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104 | * 1. The subscriptions are snapshotted just before every `dispatch()` call.
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105 | * If you subscribe or unsubscribe while the listeners are being invoked, this
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106 | * will not have any effect on the `dispatch()` that is currently in progress.
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107 | * However, the next `dispatch()` call, whether nested or not, will use a more
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108 | * recent snapshot of the subscription list.
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109 | *
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110 | * 2. The listener should not expect to see all state changes, as the state
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111 | * might have been updated multiple times during a nested `dispatch()` before
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112 | * the listener is called. It is, however, guaranteed that all subscribers
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113 | * registered before the `dispatch()` started will be called with the latest
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114 | * state by the time it exits.
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115 | *
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116 | * @param {Function} listener A callback to be invoked on every dispatch.
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117 | * @returns {Function} A function to remove this change listener.
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118 | */
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119 | function subscribe(listener) {
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120 | if (typeof listener !== 'function') {
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121 | throw new Error('Expected the listener to be a function.')
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122 | }
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123 |
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124 | if (isDispatching) {
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125 | throw new Error(
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126 | 'You may not call store.subscribe() while the reducer is executing. ' +
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127 | 'If you would like to be notified after the store has been updated, subscribe from a ' +
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128 | 'component and invoke store.getState() in the callback to access the latest state. ' +
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129 | 'See https://redux.js.org/api-reference/store#subscribelistener for more details.'
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130 | )
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131 | }
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132 |
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133 | let isSubscribed = true
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134 |
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135 | ensureCanMutateNextListeners()
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136 | nextListeners.push(listener)
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137 |
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138 | return function unsubscribe() {
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139 | if (!isSubscribed) {
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140 | return
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141 | }
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142 |
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143 | if (isDispatching) {
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144 | throw new Error(
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145 | 'You may not unsubscribe from a store listener while the reducer is executing. ' +
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146 | 'See https://redux.js.org/api-reference/store#subscribelistener for more details.'
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147 | )
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148 | }
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149 |
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150 | isSubscribed = false
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151 |
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152 | ensureCanMutateNextListeners()
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153 | const index = nextListeners.indexOf(listener)
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154 | nextListeners.splice(index, 1)
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155 | currentListeners = null
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156 | }
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157 | }
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158 |
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159 | /**
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160 | * Dispatches an action. It is the only way to trigger a state change.
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161 | *
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162 | * The `reducer` function, used to create the store, will be called with the
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163 | * current state tree and the given `action`. Its return value will
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164 | * be considered the **next** state of the tree, and the change listeners
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165 | * will be notified.
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166 | *
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167 | * The base implementation only supports plain object actions. If you want to
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168 | * dispatch a Promise, an Observable, a thunk, or something else, you need to
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169 | * wrap your store creating function into the corresponding middleware. For
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170 | * example, see the documentation for the `redux-thunk` package. Even the
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171 | * middleware will eventually dispatch plain object actions using this method.
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172 | *
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173 | * @param {Object} action A plain object representing “what changed”. It is
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174 | * a good idea to keep actions serializable so you can record and replay user
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175 | * sessions, or use the time travelling `redux-devtools`. An action must have
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176 | * a `type` property which may not be `undefined`. It is a good idea to use
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177 | * string constants for action types.
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178 | *
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179 | * @returns {Object} For convenience, the same action object you dispatched.
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180 | *
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181 | * Note that, if you use a custom middleware, it may wrap `dispatch()` to
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182 | * return something else (for example, a Promise you can await).
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183 | */
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184 | function dispatch(action) {
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185 | if (!isPlainObject(action)) {
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186 | throw new Error(
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187 | 'Actions must be plain objects. ' +
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188 | 'Use custom middleware for async actions.'
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189 | )
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190 | }
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191 |
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192 | if (typeof action.type === 'undefined') {
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193 | throw new Error(
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194 | 'Actions may not have an undefined "type" property. ' +
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195 | 'Have you misspelled a constant?'
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196 | )
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197 | }
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198 |
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199 | if (isDispatching) {
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200 | throw new Error('Reducers may not dispatch actions.')
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201 | }
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202 |
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203 | try {
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204 | isDispatching = true
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205 | currentState = currentReducer(currentState, action)
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206 | } finally {
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207 | isDispatching = false
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208 | }
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209 |
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210 | const listeners = (currentListeners = nextListeners)
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211 | for (let i = 0; i < listeners.length; i++) {
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212 | const listener = listeners[i]
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213 | listener()
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214 | }
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215 |
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216 | return action
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217 | }
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218 |
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219 | /**
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220 | * Replaces the reducer currently used by the store to calculate the state.
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221 | *
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222 | * You might need this if your app implements code splitting and you want to
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223 | * load some of the reducers dynamically. You might also need this if you
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224 | * implement a hot reloading mechanism for Redux.
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225 | *
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226 | * @param {Function} nextReducer The reducer for the store to use instead.
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227 | * @returns {void}
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228 | */
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229 | function replaceReducer(nextReducer) {
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230 | if (typeof nextReducer !== 'function') {
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231 | throw new Error('Expected the nextReducer to be a function.')
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232 | }
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233 |
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234 | currentReducer = nextReducer
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235 |
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236 | // This action has a similiar effect to ActionTypes.INIT.
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237 | // Any reducers that existed in both the new and old rootReducer
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238 | // will receive the previous state. This effectively populates
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239 | // the new state tree with any relevant data from the old one.
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240 | dispatch({ type: ActionTypes.REPLACE })
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241 | }
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242 |
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243 | /**
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244 | * Interoperability point for observable/reactive libraries.
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245 | * @returns {observable} A minimal observable of state changes.
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246 | * For more information, see the observable proposal:
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247 | * https://github.com/tc39/proposal-observable
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248 | */
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249 | function observable() {
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250 | const outerSubscribe = subscribe
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251 | return {
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252 | /**
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253 | * The minimal observable subscription method.
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254 | * @param {Object} observer Any object that can be used as an observer.
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255 | * The observer object should have a `next` method.
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256 | * @returns {subscription} An object with an `unsubscribe` method that can
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257 | * be used to unsubscribe the observable from the store, and prevent further
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258 | * emission of values from the observable.
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259 | */
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260 | subscribe(observer) {
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261 | if (typeof observer !== 'object' || observer === null) {
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262 | throw new TypeError('Expected the observer to be an object.')
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263 | }
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264 |
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265 | function observeState() {
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266 | if (observer.next) {
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267 | observer.next(getState())
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268 | }
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269 | }
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270 |
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271 | observeState()
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272 | const unsubscribe = outerSubscribe(observeState)
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273 | return { unsubscribe }
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274 | },
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275 |
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276 | [$$observable]() {
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277 | return this
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278 | }
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279 | }
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280 | }
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281 |
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282 | // When a store is created, an "INIT" action is dispatched so that every
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283 | // reducer returns their initial state. This effectively populates
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284 | // the initial state tree.
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285 | dispatch({ type: ActionTypes.INIT })
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286 |
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287 | return {
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288 | dispatch,
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289 | subscribe,
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290 | getState,
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291 | replaceReducer,
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292 | [$$observable]: observable
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293 | }
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294 | }
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