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.

InteractionManager

One reason why native apps feel so good performance wise is that barely any work is being done during an interaction/animation. In React Native, you can use InteractionManager that allows long-running work to be scheduled after any interactions/animations have completed.

Applications can schedule tasks to run after interactions with the following:

InteractionManager.runAfterInteractions(() => {
   // ...long-running synchronous task...
});

Compare this to other scheduling alternatives:

• requestAnimationFrame(): for code that animates a view over time.
• setImmediate/setTimeout/setInterval(): run code later, note this may delay animations.
• runAfterInteractions(): run code later, without delaying active animations.

The touch handling system considers one or more active touches to be an 'interaction' and will delay runAfterInteractions() callbacks until all touches have ended or been cancelled.

InteractionManager also allows applications to register animations by creating an interaction 'handle' on animation start, and clearing it upon completion:

var handle = InteractionManager.createInteractionHandle();
// run animation... (`runAfterInteractions` tasks are queued)
// later, on animation completion:
InteractionManager.clearInteractionHandle(handle);
// queued tasks run if all handles were cleared

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.