withRouter可以加工一般组件，让一般组件具备路由组件所特有的API

import React, { Component } from 'react'
// 引入withRouter
import {withRouter} from 'react-router-dom'

class Header extends Component {

    back = ()=>{
        this.props.history.goBack()
    }

    forward = ()=>{
        this.props.history.goForward()
    }

    go = ()=>{
        this.props.history.go(-2)
    }

    render() {
        console.log('Header组件收到的props是',this.props);
        return (
            <div className="page-header">
                <h2>React Router Demo</h2>
                <button onClick={this.back}>回退</button>&nbsp;
                <button onClick={this.forward}>前进</button>&nbsp;
                <button onClick={this.go}>go</button>
            </div>
        )
    }
}

export default withRouter(Header)

//withRouter可以加工一般组件，让一般组件具备路由组件所特有的API
//withRouter的返回值是一个新组件