props 可以把數據從父傳給子，如果想要實現子傳給父數據，可以把數據當成函數的參數傳遞給父組件，下面給一行代碼揣摩：
class ParentCom extends React.Component{
constructor(props){
super(props)
this.state = {
childData:null
}
}
render(){
return (
<div>
<h1>子元素傳遞過來的數據：{this.state.childData}</h1>
<ChildCom setChildData={this.setChildData}/>
</div>
)
}
setChildData = (data) => {
this.setState({
childData:data
})
}
}
class ChildCom extends React.Component{
constructor(props){
super(props)
this.state = {
msg: "helloworld"
}
}
render(){
return (
<div>
<button onClick={this.sendData}>傳遞helloword給父元素</button>
</div>
)
}
sendData = () => {
this.props.setChildData(this.state.msg)
}
}
ReactDOM.render(
<ParentCom/>,
document.getElementById('root')
)