Question

在React中，setState()是异步函数，而setTimeout()也是异步函数（有人认为，setState()可能是同步函数？），为什么setState()比setTimeout()优先执行？

componentDidMount(){
    this.setState({val: this.state.val + 1}, ()=>{
        console.log("In callback " + this.state.val);
    });
    console.log("Direct call " + this.state.val);   
    setTimeout(()=>{
        console.log("begin of setTimeout" + this.state.val);
        this.setState({val: this.state.val + 1}, ()=>{
            console.log("setTimeout setState callback " + this.state.val);
        });
        setTimeout(()=>{
            console.log("setTimeout of settimeout " + this.state.val);
        }, 0);
        console.log("end of setTimeout " + this.state.val);
    }, 0);
}

> Direct call 0
> In callback 1
> begin of setTimeout 1
> setTimeout setState callback 2
> end of setTimeout 2
> setTimeout of settimeout 2

Answer 1

无需使用setTimeout。 setState函数确实支持回调函数。

setState(updater[, callback])

在React中，为什么setState（）优先于setTimeout执行？

1 个答案: