Timers are an important part of an application and React Native implements the [browser timers](https://developer.mozilla.org/en-US/Add-ons/Code_snippets/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.

```javascript
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.