84 lines
3.3 KiB
Markdown
84 lines
3.3 KiB
Markdown
---
|
||
id: 5a24c314108439a4d403617d
|
||
title: Use the Lifecycle Method componentDidMount
|
||
challengeType: 6
|
||
isRequired: false
|
||
videoUrl: ''
|
||
localeTitle: 使用生命周期方法componentDidMount
|
||
---
|
||
|
||
## Description
|
||
<section id="description">大多数Web开发人员在某些时候需要调用API端点来检索数据。如果您正在使用React,那么知道执行此操作的位置非常重要。 React的最佳实践是在生命周期方法<code>componentDidMount()</code>中对服务器进行API调用或任何调用。将组件安装到DOM后调用此方法。此处对<code>setState()</code>任何调用都将触发组件的重新呈现。在此方法中调用API并使用API返回的数据设置状态时,一旦收到数据,它将自动触发更新。 </section>
|
||
|
||
## Instructions
|
||
<section id="instructions"> <code>componentDidMount()</code>有一个模拟API调用。它在2.5秒后设置状态以模拟调用服务器以检索数据。此示例请求站点的当前活动用户总数。在render方法中,在<code>h1</code>呈现<code>activeUsers</code>的值。观看预览中发生的事情,并随时更改超时以查看不同的效果。 </section>
|
||
|
||
## Tests
|
||
<section id='tests'>
|
||
|
||
```yml
|
||
tests:
|
||
- text: <code>MyComponent</code>应该呈现一个包含<code>h1</code>标记的<code>div</code>元素。
|
||
testString: 'assert((() => { const mockedComponent = Enzyme.mount(React.createElement(MyComponent)); return (mockedComponent.find("div").length === 1 && mockedComponent.find("h1").length === 1); })(), "<code>MyComponent</code> should render a <code>div</code> element which wraps an <code>h1</code> tag.");'
|
||
- text: 应使用<code>componentDidMount</code>的超时函数更新组件状态。
|
||
testString: 'assert((() => { const mockedComponent = Enzyme.mount(React.createElement(MyComponent)); return new RegExp("setTimeout(.|\n)+setState(.|\n)+activeUsers").test(String(mockedComponent.instance().componentDidMount)); })(), "Component state should be updated with a timeout function in <code>componentDidMount</code>.");'
|
||
- text: <code>h1</code>标记应该从<code>MyComponent</code>的状态呈现<code>activeUsers</code>值。
|
||
testString: 'async () => { const mockedComponent = Enzyme.mount(React.createElement(MyComponent)); const first = () => { mockedComponent.setState({ activeUsers: 1237 }); return mockedComponent.find("h1").text(); }; const second = () => { mockedComponent.setState({ activeUsers: 1000 }); return mockedComponent.find("h1").text(); }; assert(new RegExp("1237").test(first()) && new RegExp("1000").test(second()), "The <code>h1</code> tag should render the <code>activeUsers</code> value from <code>MyComponent</code>'s state."); }; '
|
||
|
||
```
|
||
|
||
</section>
|
||
|
||
## Challenge Seed
|
||
<section id='challengeSeed'>
|
||
|
||
<div id='jsx-seed'>
|
||
|
||
```jsx
|
||
class MyComponent extends React.Component {
|
||
constructor(props) {
|
||
super(props);
|
||
this.state = {
|
||
activeUsers: null
|
||
};
|
||
}
|
||
componentDidMount() {
|
||
setTimeout( () => {
|
||
this.setState({
|
||
activeUsers: 1273
|
||
});
|
||
}, 2500);
|
||
}
|
||
render() {
|
||
return (
|
||
<div>
|
||
<h1>Active Users: { /* change code here */ }</h1>
|
||
</div>
|
||
);
|
||
}
|
||
};
|
||
|
||
```
|
||
|
||
</div>
|
||
|
||
|
||
### After Test
|
||
<div id='jsx-teardown'>
|
||
|
||
```js
|
||
console.info('after the test');
|
||
```
|
||
|
||
</div>
|
||
|
||
</section>
|
||
|
||
## Solution
|
||
<section id='solution'>
|
||
|
||
```js
|
||
// solution required
|
||
```
|
||
</section>
|