react-native/docs/Timers.md

Timers are an important part of an application and React Native implements the browser timers.

Timers

• setTimeout, clearTimeout
• setInterval, clearInterval
• setImmediate, clearImmediate
• requestAnimationFrame, cancelAnimationFrame

requestAnimationFrame(fn) is the exact equivalent of setTimeout(fn, 0), they are triggered right after the screen has been flushed.

setImmediate is executed at the end of the current JavaScript execution block, right before sending the batched response back to native. Note that if you call setImmediate within a setImmediate callback, it will be executed right away, it won't yield back to native in between.

The Promise implementation uses setImmediate its asynchronicity primitive.

TimerMixin

We found out that the primary cause of fatals in apps created with React Native was due to timers firing after a component was unmounted. To solve this recurring issue, we introduced TimerMixin. If you include TimerMixin, then you can replace your calls to setTimeout(fn, 500) with this.setTimeout(fn, 500) (just prepend this.) and everything will be properly cleaned up for you when the component unmounts.

var { TimerMixin } = React;

var Component = React.createClass({
  mixins: [TimerMixin],
  componentDidMount: function() {
    this.setTimeout(
      () => { console.log('I do not leak!'); },
      500
    );
  }
});

We highly recommend never using bare timers and always using this mixin, it will save you from a lot of hard to track down bugs.