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HomeWeb Front-endHTML Tutorial和我一起实战 react 之 JSX_html/css_WEB-ITnose

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">&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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