import React, { PureComponent } from 'react'
export default class App extends PureComponent {     constructor(props){         super(props)         this.state = {             friends: [                 {name:"lilei",age:20},                 {name:"lily",age:25},                 {name:"tom",age:30}             ]         }     }     render() {         return (             <div>                 <h2>好友列表</h2>                 <ul>                     {                         this.state.friends.map( (item,index) => {                             return (                                 <li key={index}>                                     姓名：{item.name}，                                     年龄：{item.age}，                                     <button onClick = { e => this.incrementAge(index) }>age + 1</button>                                 </li>                                                              )                                                     })                     }                 </ul>                 <button onClick = { e => this.insertDate() }>添加数据</button>             </div>         )     }
    // shouldComponentUpdate(nextProps, nextState) {              //     if(nextState.friends !== this.state.friends){     //         return true;     //     }     //     return false;     // }       insertDate(){         let newFriends = [...this.state.friends];         newFriends.push({name:"Eric",age:28})          this.setState({             friends: newFriends         })     }
    incrementAge(index){         let newFriends = [...this.state.friends];         newFriends[index].age += 1         this.setState({             friends: newFriends         })     }
}