3.5 KiB
3.5 KiB
id | title | challengeType | isRequired | videoUrl | localeTitle |
---|---|---|---|---|---|
5a24c314108439a4d4036159 | Use the Spread Operator on Arrays | 6 | false | 在阵列上使用Spread Operator |
Description
...
扩展运算符具有各种应用程序,其中一个非常适合于从现有阵列生成新阵列的先前挑战。这是相对较新的,但常用的语法。例如,如果你有一个数组myArray
并且写: let newArray = [...myArray];
newArray
现在是myArray
的克隆。两个阵列仍然分别存在于内存中。如果你执行像newArray.push(5)
这样的变异, myArray
不会改变。 ...
有效地将 myArray
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'
组成的新数组作为最后一个值。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是生成数组的浅表副本。也就是说,它只为一维数组提供不可变的数组操作。 Instructions
Tests
tests:
- text: 'Redux存储应该存在并初始化为等于<code>[Do not mutate state!]</code> 。'
testString: 'assert((function() { const initialState = store.getState(); return ( Array.isArray(initialState) === true && initialState[0] === "Do not mutate state!"); })(), "The Redux store should exist and initialize with a state equal to <code>[Do not mutate state!]</code>.");'
- text: <code>addToDo</code>和<code>immutableReducer</code>都应该是函数。
testString: 'assert(typeof addToDo === "function" && typeof immutableReducer === "function", "<code>addToDo</code> and <code>immutableReducer</code> both should be functions.");'
- text: 在Redux存储上调度<code>ADD_TO_DO</code>类型的操作应该添加<code>todo</code> ,不应该改变状态。
testString: 'assert((function() { const initialState = store.getState(); const isFrozen = DeepFreeze(initialState); store.dispatch(addToDo("__TEST__TO__DO__")); const finalState = store.getState(); const expectedState = [ "Do not mutate state!", "__TEST__TO__DO__" ]; return( isFrozen && DeepEqual(finalState, expectedState)); })(), "Dispatching an action of type <code>ADD_TO_DO</code> on the Redux store should add a <code>todo</code> item and should NOT mutate state.");'
- text: 应使用扩展运算符返回新状态。
testString: 'getUserInput => assert(getUserInput("index").includes("...state"), "The spread operator should be used to return new state.");'
Challenge Seed
const immutableReducer = (state = ['Do not mutate state!'], action) => {
switch(action.type) {
case 'ADD_TO_DO':
// don't mutate state here or the tests will fail
return
default:
return state;
}
};
const addToDo = (todo) => {
return {
type: 'ADD_TO_DO',
todo
}
}
const store = Redux.createStore(immutableReducer);
Solution
// solution required