JSX
我们知道React使用一颗DOM对象树来描述文档,如果它是普通的对象,会是怎样?
var element = { tagName: 'div', props: { id: 'div', className: 'container' }, children: [ { tagName: 'div', props: { id: 'div1', className: 'header' }, children: [...{element}] }, { tagName: 'div', props: { id: 'div2', className: 'content' }, children: [...{element}] }, { tagName: 'div', props: { id: 'div3', className: 'footer' }, children: [...{element}] } ]}
对应的 HTML:
<div class="container"> <div class="header"></div> <div class="content"></div> <div class="footer"></div></div>
JSX给予的方式正好相反,通过书写这样类似 HTML结构,通过transformer工具将其转换成了对象,且让我们看一个不借助 JSX的写法实现上面的结构。
React.createElement( 'div', { className: 'container'}, React.createElement( 'div', { className: 'header'} ), React.createElement( 'div', { className: 'content'} ), React.createElement( 'div', { className: 'footer'} ));
开始使用JSX
在今后的编程实践中期望大家使用JSX来书写React组件
利用JSX我们现在可以像写 HTML一样来书写React组件,某些情况下在属性中你还需要注意 JavaScript的保留字,比如class属性要写成className,for需要写成htmlFor。 JSX对于大小写是敏感的,小写属于HTML标签,大写则是React组件。
使用 JSX书写一个简单的组件:
import React from 'react';import { render } from 'react-dom';function Hello (props){ const { className, children } = props; return ( <div className={ className }> { children } </div> );}render(( <Hello className="div"> Hello World </Hello>),document.getElementById('app'))
表达式
在 JSX中 {}用来表示一个 JavaScript表达式,你可以在这里进行求值逻辑或者赋值,赋值且可看上述的Hello例子,只需要 { children }。
且看我们已经实现的 Dialog根据不同的 type类型来呈现不同的子组件。
好的写法是将逻辑判断写在return之前(good):
import Alert from './Alert';import Confirm from './Confirm';class Dialog extends React.Component { render (){ const { type } = this.props; const Component = type === 'alert' ? Alert : Confirm; return ( <section> <Component {...this.props} /> </section> ); }}
当然你也可以直接将表达式写在return里面(这个写法非常不好 bad):
import Alert from './Alert';import Confirm from './Confirm';class Dialog extends React.Component { render (){ const { type } = this.props; return ( <section> { type === 'alert' ? <Alert {...this.props} /> : <Confirm {...this.props} /> } </section> ); }}
注释
在 JSX里的注视和 JavaScript一样,比如 //, /**/,唯一的要求是需要使用 {}包括起来。
{/*<Component {...this.props }/>*/}
spread attributes
在Dialog的例子中可以看见大量的 ...符号,这是属于ES2015规范中的操作符,在React组件中的 {...this.props},可以将 props的属性设置为 React Component的属性。
HTML转义和自定义属性
为了防止XSS攻击,React组件会将需要显示到DOM的字符串进行转义,如果实在有这样的需求,可以有如下的几种方式解决:
- 使用UTF-8的字符集
- 使用对应字符的Unicode编码
- 使用数组组装
- 使用原始HTML
<div>{['First ', <span key="middot">·</span>, ' Second']}</div>
如果你在JSX中使用了不存在于HTML规范的属性,这个属性是会被忽略的,你需要使用 data-方式来自定义属性。
关于支持的标签,属性,以及可访问性属性前缀的列表:
- React支持的标签,属性
- 可访问性属性前缀列表

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