javascript - react : Handling Events - parameter visibility

Question

我正在关注 React 文档。在'Handling Events ' 部分，下面的代码段就在那里。

class Toggle extends React.Component {
  constructor(props) {
    super(props);
    this.state = {isToggleOn: true};

    // This binding is necessary to make `this` work in the callback
    this.handleClick = this.handleClick.bind(this);
  }

  handleClick() {
    this.setState(state => ({
      isToggleOn: !state.isToggleOn
    }));
  }

  render() {
    return (
      <button onClick={this.handleClick}>
        {this.state.isToggleOn ? 'ON' : 'OFF'}
      </button>
    );
  }
}

ReactDOM.render(
  <Toggle />,
  document.getElementById('root')
);

在handleClick()函数中，如何访问state？为什么不this.state？

Answer 1

这就是 this.setState 的工作原理，它是为 this.setState() 传递的更新程序回调，根据 react documentation :

Passing an update function allows you to access the current state value inside the updater. Since setState calls are batched, this lets you chain updates and ensure they build on top of each other instead of conflicting

更多信息可参见here也是如此。