2018-10-10 22:03:03 +00:00
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---
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id: 5a24c314108439a4d4036172
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2021-03-05 15:43:24 +00:00
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title: 以另一种方式在用户界面中渲染状态
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2018-10-10 22:03:03 +00:00
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challengeType: 6
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2020-09-17 16:13:42 +00:00
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forumTopicId: 301408
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2021-01-13 02:31:00 +00:00
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dashedName: render-state-in-the-user-interface-another-way
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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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2021-03-05 15:43:24 +00:00
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还有另一种方法可以访问组件中的 `state`。 在 `render()` 方法中,在 `return` 语句之前,可以直接编写 JavaScript。 例如,可以声明函数、从 `state` 或 `props` 中访问数据、对此数据执行计算等。 然后,可以将任何数据赋值给 `return` 语句中可以访问的变量。
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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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2021-03-05 15:43:24 +00:00
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在 `MyComponent` 的 render 方法中,定义一个名为 `name` 的 `const`(常量),并将其设置为组件 `state` 中的 name 值。 因为可以直接在代码部分编写 JavaScript,所以不需要用大括号括起来。
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2018-10-10 22:03:03 +00:00
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2021-03-05 15:43:24 +00:00
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接下来,在 return 语句中,在 `h1` 标签中渲染变量 `name` 的值。 记住,在 return 语句中需要使用 JSX 语法(用到 JavaScript 的花括号)。
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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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2021-03-05 15:43:24 +00:00
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`MyComponent` 应该有一个键 `name`,其值 `freeCodeCamp` 存储在其 state 中。
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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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assert(
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Enzyme.mount(React.createElement(MyComponent)).state('name') ===
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'freeCodeCamp'
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);
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2018-10-10 22:03:03 +00:00
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```
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2021-03-05 15:43:24 +00:00
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`MyComponent` 应该在 `div` 中渲染一个 `h1` 标题。
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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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/<div><h1>.*<\/h1><\/div>/.test(
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Enzyme.mount(React.createElement(MyComponent)).html()
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)
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);
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```
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2021-03-05 15:43:24 +00:00
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渲染的 `h1` 标签应该包含 `{name}` 的引用。
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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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(getUserInput) =>
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assert(/<h1>\n*\s*\{\s*name\s*\}\s*\n*<\/h1>/.test(getUserInput('index')));
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```
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2018-10-10 22:03:03 +00:00
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2021-03-05 15:43:24 +00:00
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渲染的 `h1` 标题中应该包含一段文本,这段文本是从组件的 state 中渲染出来的。
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2020-09-17 16:13:42 +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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async () => {
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const waitForIt = (fn) =>
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new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 250));
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const mockedComponent = Enzyme.mount(React.createElement(MyComponent));
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const first = () => {
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mockedComponent.setState({ name: 'TestName' });
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return waitForIt(() => mockedComponent.html());
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};
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const firstValue = await first();
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assert(firstValue === '<div><h1>TestName</h1></div>');
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2020-09-17 16:13:42 +00:00
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};
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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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## --after-user-code--
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```jsx
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ReactDOM.render(<MyComponent />, document.getElementById('root'))
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```
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## --seed-contents--
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```jsx
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class MyComponent 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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name: 'freeCodeCamp'
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}
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}
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render() {
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// Change code below this line
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// Change code above this line
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return (
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<div>
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{ /* Change code below this line */ }
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{ /* Change code above this line */ }
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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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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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```jsx
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class MyComponent 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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name: 'freeCodeCamp'
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}
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}
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render() {
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// Change code below this line
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const name = this.state.name;
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// Change code above this line
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return (
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<div>
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{ /* Change code below this line */ }
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<h1>{name}</h1>
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{ /* Change code above this line */ }
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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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