115 lines
2.4 KiB
Markdown
115 lines
2.4 KiB
Markdown
---
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id: 5a24c314108439a4d403615a
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title: 從數組中刪除項目
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challengeType: 6
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forumTopicId: 301447
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dashedName: remove-an-item-from-an-array
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---
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# --description--
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是時候練習從數組中刪除項目了。 擴展運算符也可以在這裏使用。 其他有用的JavaScript方法包括 `slice()` 和 `concat()`。
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# --instructions--
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reducer 和 action creator 被修改爲根據項目的索引從數組中刪除一個項目。 完成編寫 reducer 以便返回一個新的狀態數組，並刪除特定索引處的項目。
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# --hints--
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Redux store 應該存在並初始化一個 `[0,1,2,3,4,5]` 的狀態。
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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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DeepEqual(initialState, [0, 1, 2, 3, 4, 5])
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);
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})()
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);
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```
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`removeItem` 和 `immutableReducer` 都應該是一個函數。
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```js
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assert(
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typeof removeItem === 'function' && typeof immutableReducer === 'function'
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);
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```
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dispatch `removeItem` action creator 應該從 state 中刪除項目，不應該改變 state。
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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(removeItem(3));
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const state_1 = store.getState();
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store.dispatch(removeItem(2));
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const state_2 = store.getState();
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store.dispatch(removeItem(0));
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store.dispatch(removeItem(0));
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store.dispatch(removeItem(0));
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const state_3 = store.getState();
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return (
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isFrozen &&
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DeepEqual(state_1, [0, 1, 2, 4, 5]) &&
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DeepEqual(state_2, [0, 1, 4, 5]) &&
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DeepEqual(state_3, [5])
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);
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})()
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);
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```
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# --seed--
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## --seed-contents--
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```js
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const immutableReducer = (state = [0,1,2,3,4,5], action) => {
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switch(action.type) {
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case 'REMOVE_ITEM':
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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 removeItem = (index) => {
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return {
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type: 'REMOVE_ITEM',
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index
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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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# --solutions--
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```js
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const immutableReducer = (state = [0,1,2,3,4,5], action) => {
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switch(action.type) {
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case 'REMOVE_ITEM':
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return [
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...state.slice(0, action.index),
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...state.slice(action.index + 1)
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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 removeItem = (index) => {
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return {
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type: 'REMOVE_ITEM',
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index
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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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