129 lines
4.3 KiB
Markdown
129 lines
4.3 KiB
Markdown
---
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id: 5a24c314108439a4d4036177
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challengeType: 6
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forumTopicId: 301425
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title: 写一个简单的计数器
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---
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## Description
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<section id='description'>
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你可以结合目前为止所涵盖的概念来设计更复杂的有状态组件。这包括初始化<code>state</code>，编写设置<code>state</code>的方法，以及指定单击处理程序来触发这些方法。
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</section>
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## Instructions
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<section id='instructions'>
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<code>Counter</code>组件跟踪<code>state</code>中的<code>count</code>值。有两个按钮分别调用<code>increment()</code>和<code>decrement()</code>方法。编写这些方法，使计数器值在单击相应按钮时增加或减少 1。另外，创建一个<code>reset()</code>方法，当单击 reset 按钮时，把计数设置为 0。
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<strong>注意：</strong> 确保你没有修改按钮的<code>classNames</code>。另外，请记住在构造函数中为新创建的方法添加必要的绑定。
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: <code>Counter</code>应该返回一个<code>div</code>元素，它包含三个按钮，按钮内容依次是<code>Increment!</code>、<code>Decrement!</code>、<code>Reset</code>。
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testString: assert((() => { const mockedComponent = Enzyme.mount(React.createElement(Counter)); return (mockedComponent.find('.inc').text() === 'Increment!' && mockedComponent.find('.dec').text() === 'Decrement!' && mockedComponent.find('.reset').text() === 'Reset'); })());
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- text: <code>Counter</code>应该使用设置为<code>0</code>的<code>count</code>属性初始化 state。
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testString: 'const mockedComponent = Enzyme.mount(React.createElement(Counter)); assert(mockedComponent.find("h1").text() === "Current Count: 0")'
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- text: 单击 increment 按钮应将计数增加<code>1</code>。
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testString: 'const mockedComponent = Enzyme.mount(React.createElement(Counter)); mockedComponent.find(".inc").simulate("click"); assert(mockedComponent.find("h1").text() === "Current Count: 1")'
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- text: 单击 decrement 按钮应将计数减少<code>1</code>。
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testString: 'const mockedComponent = Enzyme.mount(React.createElement(Counter)); mockedComponent.find(".dec").simulate("click"); assert(mockedComponent.find("h1").text() === "Current Count: -1")'
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- text: 单击 reset 按钮应将计数重置为<code>0</code>。
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testString: 'const mockedComponent = Enzyme.mount(React.createElement(Counter)); mockedComponent.setState({ count: 5 }); const currentCountElement = mockedComponent.find("h1"); assert(currentCountElement.text() === "Current Count: 5"); mockedComponent.find(".reset").simulate("click"); assert(currentCountElement.text() === "Current Count: 0");'
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='jsx-seed'>
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```jsx
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class Counter extends React.Component {
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constructor(props) {
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super(props);
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this.state = {
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count: 0
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};
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// change code below this line
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// change code above this line
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}
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// change code below this line
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// change code above this line
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render() {
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return (
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<div>
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<button className='inc' onClick={this.increment}>Increment!</button>
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<button className='dec' onClick={this.decrement}>Decrement!</button>
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<button className='reset' onClick={this.reset}>Reset</button>
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<h1>Current Count: {this.state.count}</h1>
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</div>
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);
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}
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};
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```
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</div>
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### After Test
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<div id='jsx-teardown'>
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```js
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ReactDOM.render(<Counter />, document.getElementById('root'))
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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class Counter extends React.Component {
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constructor(props) {
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super(props);
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this.state = {
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count: 0
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};
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this.increment = this.increment.bind(this);
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this.decrement = this.decrement.bind(this);
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this.reset = this.reset.bind(this);
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}
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reset() {
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this.setState({
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count: 0
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});
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}
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increment() {
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this.setState(state => ({
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count: state.count + 1
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}));
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}
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decrement() {
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this.setState(state => ({
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count: state.count - 1
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}));
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}
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render() {
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return (
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<div>
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<button className='inc' onClick={this.increment}>Increment!</button>
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<button className='dec' onClick={this.decrement}>Decrement!</button>
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<button className='reset' onClick={this.reset}>Reset</button>
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<h1>Current Count: {this.state.count}</h1>
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</div>
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);
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}
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};
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```
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</section>
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