（二）回调形式的 ref

class Demo {
    render() {
        return(
            <div>
                <input ref={() => {console.log('@')}}/>
                
                <input ref={(a) => {console.log(a)}}/>

                <input ref={(a) => {this.input1 = a}}/>
            </div>
        )
    }
}

ReactDOM.render(<Demo/>, document.getElmentById('test'))

class Demo extends React.Component{
    showData = () => {
        let {input1} = this
        alert(input1.value)
    }

    showData2 = () => {
        let {input2} = this
        alert(input1.value)
    }

    render() {
        return (
            <div>
                <input ref={C = this.input1 = C} type="text" placeholder="点击按钮提示数据"/>
                <button onClick="this.showData">点我提示左侧的数据</button>
                <input onBlur={this.showData2} type="text" placeholder="失去焦点提示数据"/>
            </div>
        )
    }
}

ReactDOM.render(<Demo/>, document.getElmentByID('test'))