2018-10-10 22:03:03 +00:00
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---
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id: 5a24c314108439a4d4036159
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2021-03-07 16:15:14 +00:00
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title: 在数组中使用扩展运算符
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2018-10-10 22:03:03 +00:00
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challengeType: 6
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2020-09-07 08:16:17 +00:00
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forumTopicId: 301452
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2021-01-13 02:31:00 +00:00
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dashedName: use-the-spread-operator-on-arrays
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2018-10-10 22:03:03 +00:00
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---
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2020-12-16 07:37:30 +00:00
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# --description--
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2018-10-10 22:03:03 +00:00
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2021-03-07 16:15:14 +00:00
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ES6 中有助于在 Redux 中强制执行状态不变性的一个解决方案是扩展运算符:`...`。 扩展运算符具有很多的应用,其中一种非常适合通过一个已有的数组生成一个新数组。 这是相对较新的但常用的语法。 例如,如果你有一个数组 `myArray` 并写:
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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`let newArray = [...myArray];`
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2018-10-10 22:03:03 +00:00
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2021-03-07 16:15:14 +00:00
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`newArray` 现在是 `myArray` 的克隆。 两个数组仍然在内存中单独存在。 如果你执行像 `newArray.push(5)` 这样的代码,`myArray` 不会改变。 `...` 有效将 `myArray` 中的值 *展开*到一个新数组中。 要克隆数组但在新数组中添加其他值,可以编写 `[...myArray, 'new value']`。 这将返回一个由 `myArray` 中的值和字符串 `new value` (作为最后一个值)组成的新数组。 扩展语法可以像这样在数组组合中多次使用,但重要的是要注意它只做一个浅拷贝。 这就是说,它只为一维数组提供了不可变的数组操作。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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# --instructions--
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2018-10-10 22:03:03 +00:00
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2021-03-07 16:15:14 +00:00
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添加待办事项时,使用 spread 运算符返回新的状态副本。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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# --hints--
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2018-10-10 22:03:03 +00:00
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2021-03-07 16:15:14 +00:00
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Redux store 应该在代码编辑器中存在并使用 `["Do not mutate state!"]` 进行状态初始化。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert(
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(function () {
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const initialState = store.getState();
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return (
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Array.isArray(initialState) === true &&
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initialState[0] === 'Do not mutate state!'
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);
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})()
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);
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2018-10-10 22:03:03 +00:00
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```
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2021-03-07 16:15:14 +00:00
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`addToDo`和`immutableReducer`都应该是一个函数。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert(typeof addToDo === 'function' && typeof immutableReducer === 'function');
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```
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2018-10-10 22:03:03 +00:00
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2021-03-07 16:15:14 +00:00
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在 Redux store 上 dispatch 一个类型为`ADD_TO_DO` aciton 应该添加一个`todo`项,并且不应该改变 state。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert(
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(function () {
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const initialState = store.getState();
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const isFrozen = DeepFreeze(initialState);
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store.dispatch(addToDo('__TEST__TO__DO__'));
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const finalState = store.getState();
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const expectedState = ['Do not mutate state!', '__TEST__TO__DO__'];
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return isFrozen && DeepEqual(finalState, expectedState);
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})()
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);
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```
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2018-10-10 22:03:03 +00:00
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2021-03-07 16:15:14 +00:00
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应使用扩展运算符返回新的 state。
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2020-09-07 08:16:17 +00:00
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2018-10-10 22:03:03 +00:00
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```js
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2020-12-16 07:37:30 +00:00
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(getUserInput) => assert(getUserInput('index').includes('...state'));
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2018-10-10 22:03:03 +00:00
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```
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2020-08-13 15:24:35 +00:00
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2021-01-13 02:31:00 +00:00
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# --seed--
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## --seed-contents--
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```js
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const immutableReducer = (state = ['Do not mutate state!'], action) => {
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switch(action.type) {
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case 'ADD_TO_DO':
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// Don't mutate state here or the tests will fail
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return
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default:
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return state;
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}
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};
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const addToDo = (todo) => {
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return {
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type: 'ADD_TO_DO',
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todo
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}
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}
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const store = Redux.createStore(immutableReducer);
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```
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2020-12-16 07:37:30 +00:00
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# --solutions--
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2021-01-13 02:31:00 +00:00
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```js
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const immutableReducer = (state = ['Do not mutate state!'], action) => {
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switch(action.type) {
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case 'ADD_TO_DO':
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return [
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...state,
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action.todo
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];
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default:
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return state;
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}
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};
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const addToDo = (todo) => {
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return {
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type: 'ADD_TO_DO',
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todo
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}
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}
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const store = Redux.createStore(immutableReducer);
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```
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