react 基本语法

作者: 不染事非 | 来源:发表于2019-04-19 20:59 被阅读0次

一、html模板

<!DOCTYPE html>
<html>
  <head>
<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<!-- 生产环境中不建议使用 -->
<script src="https://unpkg.com/babel-standalone@6.15.0/babel.min.js"></script>
  </head>
  <body>
    <div id="example"></div>
    // script的类型必须是text/babel
    <script type="text/babel">
     // todo
    </script>
  </body>
</html>

二、ReactDOM.render()

作用: 编译模板,把模板挂载到指定的节点上

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
    <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
    <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
    <div id="root">

    </div>
</body>

</html>

<script type="text/babel">
    ReactDOM.render(
        <h1>hello world</h1>,
        document.getElementById('root')
    )
</script>

三、JSX 语法

说明: jsx语法html代码和js代码可以混写而不需要加引号,可以这样做的原因是React和到jsx代码后会进行编译,使代码正确运行.当然jsx也是有它自己本身的规则:

js代码需要用{}括起来
React编译规则: 遇到<开头就看作是html,遇到{开头则视为js

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
    <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
    <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
    <div id="root"></div>
</body>

</html>

<script type="text/babel">
    const person = {
        name: 'huruqing',
        age: 108
    }; 
    const element = 
        <h1>
            <p>姓名: {person.name}</p>
            <p>年龄: {person.age}岁</p>
        </h1>;

        ReactDOM.render( 
            element, 
            document.getElementById('root')
        );
</script>

四、组件

用es5定义一个react组件

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title></title>
    <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
    <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
    <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
    <div id="root">

    </div>
</body>

</html>

<script type="text/babel">
    // es5组件的写法,一个函数就是一个组件
    function Welcome(props) {
      return (
            <h1>
                <p>姓名: {props.person.name}</p>
                <p>年龄: {props.person.age}</p>
            </h1>
        )
    }

    const person = {
        name: 'huruqing',
        age: 108
    }
    ReactDOM.render(
        <Welcome person={person} />,
        document.getElementById('root')
    )
</script>

es6的class和class继承

<script>
/**
 * 面向对象中的继承
 * es6中的类和类的继承
 */

 // 定义一个类
 class Person {
    // 构造器(初始化类的实例)
    constructor() {
        // alert('哈哈哈哈');
        this.mouth = '1张';
        this.leg = '两条';
    }

    eat() {
        console.log('人类是个吃货');
    }

    speak() {
        console.log('会说人话');
    }
 }
 var person = new Person();
 console.log(person);

 // 继承

 class Man extends Person {
     constructor(name,age) {
        // 执行父类构造器
        super();
        this.name = name;
        this.age = age;
     }
 }

 var man = new Man('张三',100);
 console.log(man);
 console.log(man.leg);
 man.speak();

</script>

用es6定义个react组件

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title></title>
    <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
    <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
    <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
    <div id="root">

        <h1>
            <p>姓名: </p>
            <p>年龄: </p>
        </h1>
    </div>
</body>

</html>

<script type="text/babel">
    /**
        * es6使用class的形式来创建组件,继承React的Component类,
        * 后面我们更多的使用这种方式来创建组件
     */ 
    class Welcome extends React.Component {
        constructor(props) {
            super(props);
        }
        render() {
            return (
                <h1>
                    <p>姓名: {this.props.person.name}</p>
                    <p>年龄: {this.props.person.age} </p>
                </h1>
            )
        }
    }

    const person = {
        name: 'huruqing',
        age: 108
    }
    ReactDOM.render(
        <Welcome person={person} />,
        document.getElementById('root')
    )
</script>

五、props和纯函数

相同的输入有相同的输出,输入可以确定输出,这就是纯函数
对待props就像对待纯函数一样,遵循可以通过输入确定输出

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title></title>
    <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
    <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
    <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
    <div id="app">

    </div>
</body>

</html>

<script type="text/babel">
    // 这是个纯函数,输入什么,得到什么是一定的,同样的输入必定有同样的输出
    const sum = (a, b) => {
        return a + b; 
    }
    sum(2,3); // 5
    sum(2,3); // 5

    // 这个函数是不纯的,因为它修改了外部传进来的参数
    let count = 0;
    const getResult = (num) => {
        count++;
      return num*num + count;
    }
        getResult(2); // 5
        getResult(2); // 6
    // 所有的react组件都必须遵守的一条规则: 
    // 对待props就像对待纯函数一样,遵循可以通过输入确定输出
</script>

六、绑定事件

事件绑定的函数的this的指向会改变,需要使用bind来绑定函数的指向

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title></title>
    <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
    <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
    <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
    <div id="app">

    </div>
</body>

</html>

<script type="text/babel">
    class Demo extends React.Component {
      constructor(props) {
          super(props);
          // 让函数的this指向class的实例
          this.handleClick = this.handleClick.bind(this);
      }

      handleClick (){
        this.getList();
      }

      getList() {
          alert('获取列表数据');
      }

      render() {
        return (
            <div>
                <button onClick={this.handleClick}>
                click
              </button>
            </div>
        );
      }
    }

ReactDOM.render(
    <Demo />,
    document.getElementById('app')
)
</script>

事件传参的方式
react可以在{} 里面执行一个函数的调用

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title></title>
    <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
    <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
    <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
    <div id="root">

    </div>
</body>

</html>

<script type="text/babel">
    class Demo extends React.Component {
        constructor(props) {
            super(props);
            this.toDetail = this.toDetail.bind(this);
        }

    toDetail(id) {
        console.log(event);
        alert(id);
    }

    render() {
        return (
            <div>
                <ul>
                    <li> <button onClick={() => {this.toDetail(1001)}}>电影1</button> </li>
                    <li> <button onClick={() => {this.toDetail(1002)}}>电影2</button> </li>
                    <li> <button onClick={() => {this.toDetail(1003)}}>电影3</button> </li>
                </ul>
            </div>
        )
    }
}

ReactDOM.render(
    <Demo />,
    document.getElementById('root')
)
</script>

七、列表渲染

<!DOCTYPE html>
<html>

<head>
  <meta charset="UTF-8">
  <title></title>
  <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
  <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
  <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
  <div id="root">

  </div>
</body>

</html>

<script type="text/babel">
  class List extends React.Component {
   constructor(props) {
     super(props);
   }

   render() {
    let heroList = this.props.heroList;
    return (
      <ul>
        {heroList.map(hero =>{
            return (
                <li key={hero.id}>
                  {hero.heroName} -- {hero.role}
                </li>
              )
            }
        )}
      </ul>
    )
   }
}

const heroList = [
  {id: 1, heroName: '亚瑟', role: '战士'},
  {id: 2, heroName: '牛魔王', role: '战士'},
  {id: 3, heroName: '鲁班七号', role: '射手'}
];

ReactDOM.render(
<List heroList={heroList} />,
  document.getElementById('root')
);   

</script>

八、条件渲染

通过 if 来控制渲染内容

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title></title>
   <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
   <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
   <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
    <div id="app">

    </div>
</body>

</html>

<script type="text/babel">

class Welcome extends React.Component {
   constructor(props) {
       super(props);
   }

   render() {
       // 使用if else判断变量isLogin的值来决定显示什么内容
       if (this.props.isLogin) {
           return (
               <h1>欢迎回来, <button style={{color: 'blue'}}>退出登录</button></h1>
           )
       } else {
           return (
               <h1>你还没登录, <button  style={{color: 'red'}}>请登录</button></h1>
           )
       }
   }    

}

ReactDOM.render(
   <Welcome isLogin={false}/>,
   document.getElementById('app') 
)
</script>

通过三目运算符来判断
使用三目运算符判断变量isLogin的值来决定显示什么内容

<!DOCTYPE html>
<html>

<head>
  <meta charset="UTF-8">
  <title>三目运算符</title>
  <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
  <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
  <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
  <div id="app">

  </div>
</body>

</html>

<script type="text/babel">

class Welcome extends React.Component {
   constructor(props) {
       super(props);
   }

   render() {
       /**
       * 通过变量isLogin来决定显示什么内容
       * 使用三目运算符(内容较短用三目运算符)
       * 再长一点用上面if else的方式
       * 更长的内容封装成一个组件更合适
       */
      return (
        this.props.isLogin?
        <h1>欢迎回来, <button style={{color: 'blue'}}>退出登录</button></h1>:
         <h1>你还没登录, <button  style={{color: 'red'}}>请登录</button></h1>
      )
   }    

}

ReactDOM.render(
   <Welcome isLogin={true}/>,
   document.getElementById('app') 
)

</script>

通过与运算符 && 进行控制
相当于if没有else的情况

<!DOCTYPE html>
<html>

<head>
  <meta charset="UTF-8">
  <title>三目运算符</title>
  <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
  <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
  <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
  <div id="app">

  </div>
</body>

</html>

<script type="text/babel">

class Welcome extends React.Component {
   constructor(props) {
       super(props);
   }

   render() {
       /**
       * 如果值为true就显示,为false不显示,相当于vue的v-show
       */
      return (
        this.props.show && 
          <p>
            React 起源于 Facebook 的内部项目，因为该公司对市场上所有 JavaScript MVC 框架，都不满意，就决定自己写一套，用来架设 Instagram
            的网站。做出来以后，发现这套东西很好用，就在2013年5月开源了。
          </p>
      )
   }    

}

ReactDOM.render(
   <Welcome show={true}/>,
   document.getElementById('app') 
)
</script>

九、this.state和this.setState

例1

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <!-- react框架文件 -->
    <script src="lib/react.development.js"></script>
    <!-- react用来渲染页面的文件 -->
    <script src="lib/react-dom.development.js"></script>
    <!-- 用来编译jsx语法的库 -->
    <script src="lib/babel.min.js"></script>
</head>

<body>
    <div id="app">

    </div>

    <script type="text/babel">
        class Login extends React.Component {
            constructor(props) {
                super(props);
                this.login = this.login.bind(this);
                this.logout = this.logout.bind(this);
                this.state = {
                    isLogin: false
                }
            }

            render() {
                let { isLogin } = this.state;
                return (
                    <div>
                        {isLogin?<p>****5539<button onClick={this.logout}>退出登陆</button></p>:<button onClick={this.login}>立即登陆</button>}
                    </div>
                )
            }

            logout() {
                this.setState({
                    isLogin: false
                })
            }

            login() {
                this.setState({
                    isLogin: true
                })
            }
        }

        ReactDOM.render(
            <Login/>,
            document.getElementById('app')
        )
    </script>
</body>

</html>

例2

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title>三目运算符</title>
    <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
     <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
     <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
    <div id="app">

    </div>
</body>

</html>

<script type="text/babel">

class Welcome extends React.Component {
   constructor(props) {
       super(props);
    // state的初始值
    this.state = {
         show: true
    }
    this.toggleMsg = this.toggleMsg.bind(this);
   }

toggleMsg(flag) {
  // 修改state里show的值
    this.setState({
        show: flag
   })
}

   render() {
      return (
        <div>
        <button onClick={()=> {this.toggleMsg(true)}}>显示</button>
        <button onClick={()=> {this.toggleMsg(false)}}>隐藏</button>
        <hr />
        {this.state.show && 
                <p>React 起源于 Facebook 的内部项目，因为该公司对市场上所有 JavaScript MVC       
                      框架，都不满意，就决定自己写一套，用来架设 Instagram
                      的网站。做出来以后，发现这套东西很好用，就在2013年5月开源了。
                  </p>
        }
        </div>
      )
   }    
}

ReactDOM.render(
   <Welcome />,
   document.getElementById('app') 
)
</script>

十、样式和属性

class使用className代替
style需要用{{}},外面的{}代表这是js代码,里面的{}则是个js对象
属性是个变量加上{}即可

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title></title>
     <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
     <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
     <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
    <style>
        .green {
            color: green;
        }
    </style>
</head>

<body>
    <div id="root">

    </div>
</body>

</html>

<script type="text/babel">
    let bg = '#999';
    let imgUrl = 'https://ss2.baidu.com/6ONYsjip0QIZ8tyhnq/it/u=1598000148,3084276147&fm=58&s=36F6EC36C8A47E92227DC7C502007026';

    ReactDOM.render(
        <div>
            <p style={{backgroundColor: bg,width: '200px'}}>hello react</p>
            <p className="green">我的react</p>
            <img src={imgUrl}/>
        </div>,

        document.getElementById('root')
    )
</script>

十一、生命周期

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title></title>
  <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
  <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
  <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
    <div id="root">

    </div>
</body>

</html>

<script type="text/babel">
    /**
 * react的生命周期分成三种
 * 1\. mount 挂载
 * 2\. update 更新
 * 3\. unmount 卸载
 */

 class Hello extends React.Component {

    componentWillMount() {
        console.log('即将挂载');
    }

    componentDidMount() {
        console.log('已挂载');
    }

    componentWillUpdate(nextProps, nextState) {
        console.log('将要更新');
    }

    componentDidUpdate(prevProps, prevState) {
        console.log('更新完毕');
    }

    // 默认每一次的修改都触发页面更新,此函数用于干预是否要更新,用于性能优化,
    shouldComponentUpdate(nextProps, nextState) {

    }

    componentWillUnmount() {
        console.log('将要卸载');
    }

    render() {
        return <div>生命周期</div>
    }
 }

ReactDOM.render(
  <Hello name="world"/>,
  document.getElementById('root')
);
</script>

十二、表单

单个input标签输入,让输入的数据与react数据流同步

<!DOCTYPE html>
<html>

<head>
  <meta charset="UTF-8">
  <title></title>
  <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
  <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
  <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
  <div id="root">

  </div>
</body>

</html>

<script type="text/babel">

class NameForm extends React.Component {
  constructor(props) {
    super(props);
    this.state = {value: ''};

    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleChange(event) {
    this.setState({value: event.target.value});
  }

  handleSubmit(event) {
    alert('你输入的用户名是: ' + this.state.value);
    event.preventDefault();
  }

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <p>
          用户名:
          <input type="text" value={this.state.value} onChange={this.handleChange} />
        </p>
        <input type="submit" value="提交" />
      </form>
    );
  }
}

ReactDOM.render(
  <NameForm />,
  document.getElementById('root')
)
</script>

多个input表单输入
如果有多个input标签输入,我们是否需要为每一个input绑定一个事件呢,会不会太麻烦了,
其实不用,我们可以像下面这样来处理

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title></title>
    <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
    <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
    <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
    <div id="root">

    </div>
</body>

</html>

<script type="text/babel">
class Reservation extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      username: 'huruqing',
      password: 123456,
            msg: ''
    };

    this.handleChange = this.handleChange.bind(this);
  }

  handleChange(event) {
    const target = event.target;
    const value = target.value;
    const name = target.name;

    this.setState({
      [name]: value
    });
  }

  render() {
    return (
            <div>
                 <form>
                        <label>
                            用户名:
                            <input
                                name="username"
                                type="text"
                                value={this.state.username}
                                onChange={this.handleChange} />
                        </label>
                        <br />
                        <label>
                            密码:
                            <input
                                name="password"
                                type="text"
                                value={this.state.password}
                                onChange={this.handleChange} />
                        </label>
                    </form>
                    <p>
                        你输入的用户名是: {this.state.username} <br/>
                        你输入的密码是:   {this.state.password}
                    </p>
            </div>
    );
  }
}

ReactDOM.render(
  <Reservation />,
  document.getElementById('root')
)
</script>

十三、获取真实的DOM节点

通过ref可以获取真实dom节点,需要确保节点已经挂载

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title></title>
    <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
    <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
    <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
    <div id="root">

    </div>
</body>

</html>

<script type="text/babel">
    class MyComponent extends React.Component {
        constructor(props) {
            super(props);
            this.handleClick = this.handleClick.bind(this);
        }
        handleClick() {
            this.refs.myTextInput.focus();
        }
        render() {
            return (
                <div>
                    <input type="text" ref="myTextInput" />
                    <input type="button" value="获取焦点" onClick={this.handleClick} />
                </div>
            )
        }
}

ReactDOM.render(
    <MyComponent />,
    document.getElementById('root')
);
</script>

十四、this.props.children

this.props 对象的属性与组件的属性一一对应，但是有一个例外，就是 this.props.children 属性。它表示组件的所有子节点

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title></title>
    <script src="https://cdn.bootcss.com/react/16.4.0/umd/react.development.js"></script>
    <script src="https://cdn.bootcss.com/react-dom/16.4.0/umd/react-dom.development.js"></script>
    <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
    <div id="root">

    </div>
</body>

</html>

<script type="text/babel">
class NotesList extends React.Component {
    constructor(props) {
        super(props);
    }

    render() {
        return (
      <ol>
      {
        React.Children.map(this.props.children, function (child) {
          return <li>{child}</li>;
        })
      }
      </ol>
    );
    }
}

ReactDOM.render(
  <NotesList>
    <span>hello</span>
    <span>world</span>
  </NotesList>,
  document.body
);
</script>

demo地址:

参考:
React 入门实例教程 http://www.ruanyifeng.com/blog/2015/03/react.html
React中文文档 https://react.docschina.org/docs/hello-world.html