javascript - React.js 的 this.setState() 是同步还是异步？

Question

请查看以下代码。我尝试在另一个下面调用 setState 。看起来第二次调用 setState 返回的 count 始终设置为 this.state.count。在这里，它总是被分配 3

    class Counter extends React.Component {
    constructor(props){
        super(props);
        this.handleReset = this.handleReset.bind(this);
        this.state = {
            count : 0
        };
    }

    handleReset() {
        this.setState(() => {
            return {
                count: 1
            }
        });
        this.setState(() => {
            return {
                count: 3
            }
        });
    }
    render() {
        return (
            <div> 
                <h1>Count:{this.state.count}</h1>
                <button onClick={this.handleReset}>reset</button>
            </div>
        );
    }
  }
  ReactDOM.render(<Counter />, document.getElementById('app'));

Answer 1

根据 React 文档，它可以是异步的。

React may batch multiple setState() calls into a single update for performance. Because this.props and this.state may be updated asynchronously, you should not rely on their values for calculating the next state

(original source, and correct code example)