关于react的疑惑_3

在菜鸟上学react的时候看到一段代码

<script type="text/babel">
class Hello extends React.Component {
 
  constructor(props) {
      super(props);
      this.state = {opacity: 1.0};
  }
 
  componentDidMount() {
    this.timer = setInterval(function () {
      var opacity = this.state.opacity;
      opacity -= .05;
      if (opacity < 0.1) {
        opacity = 1.0;
      }
      this.setState({
        opacity: opacity
      });
    }.bind(this), 100);
  }
 
  render () {
    return (
      <div style={{opacity: this.state.opacity}}>
        Hello {this.props.name}
      </div>
    );
  }
}
 
ReactDOM.render(
  <Hello name="world"/>,
  document.body
);
</script>

主要是它里面的

componentDidMount() {
    this.timer = setInterval(function () {
      var opacity = this.state.opacity;
      opacity -= .05;
      if (opacity < 0.1) {
        opacity = 1.0;
      }
      this.setState({
        opacity: opacity
      });
    }.bind(this), 100);//this绑定在这里？？？？？？
  }

这里this是绑定在这里我就有点疑惑了，因为这个bind是在setInterval里面的而且还是绑定到了里面的函数里，那么这个里面的this不就会变成window么？？？