javascript - setTimeout in React Native

Question

I'm trying to load a splash screen for an iOS app built in React Native. I'm trying to accomplish this through class states and then a setTimeout function as follows:

class CowtanApp extends Component {
  constructor(props){
    super(props);
    this.state = {
      timePassed: false
    };
  }

  render() {
    setTimeout(function(){this.setState({timePassed: true})}, 1000);
    if (!this.state.timePassed){
      return <LoadingPage/>;
    }else{
      return (
        <NavigatorIOS
          style = {styles.container}
          initialRoute = {{
            component: LoginPage,
            title: 'Sign In',
          }}/>
      );
    }
  }
}

The loading page works for a second, and then I guess when setTimeout tries to change the state to true, my program crashes: 'undefined is not an object (evaluating this.setState)'. I've been going at this for a couple of hours, any ideas on how to fix it?

Answer 1

Classic javascript mistake.

setTimeout(function(){this.setState({timePassed: true})}, 1000)

When setTimeout runs this.setState, this is no longer CowtanApp, but window. If you define the function with the => notation, es6 will auto-bind this.

setTimeout(() => {this.setState({timePassed: true})}, 1000)

Alternatively, you could use a let that = this; at the top of your render, then switch your references to use the local variable.

render() {
  let that = this;
  setTimeout(function(){that.setState({timePassed: true})}, 1000);

If not working, use bind.

setTimeout(
  function() {
      this.setState({timePassed: true});
  }
  .bind(this),
  1000
);