javascript - React setState回调执行顺序

Question

  var SubOne = React.createClass({
    getInitialState(){
      return {
        current : 0
      };
    },

    render() {
      var that = this;
      var list = [
        1111,2222,3333,444
      ];
      var createItem = function(itemText, index) {
        return <li key={index} data-index={index} onClick={that._handleClick}>{itemText}</li>;
      };

      return <ul ref="list">{list.map(createItem)}</ul>;
    },

    componentDidMount(){
      var that = this;

      setTimeout(function(){
        that._handleClick();
      }, 2000);
    },

    _handleClick(){
      console.log("before setState");
      this.setState({
        current : 0
      },function(){
        console.log("setState callback");
      });
      console.log("after setState");
    }
  });

  React.render(<SubOne />, document.getElementById("example"));

结果是:

setTimeout 调用:

设置状态之前设置状态回调设置状态后

onclick 调用:

设置状态之前设置状态后setState回调

为什么执行顺序不同？

Answer 1

这与React的批量更新机制有关。我对这个话题并不擅长，所以我不能给你一个明确的答案，但也许这里的讨论会给你带来一些启发:) https://groups.google.com/forum/#!topic/reactjs/LkTihnf6Ey8