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PouchDB has an asynchronous API, supporting [callbacks](http://docs.nodejitsu.com/articles/getting-started/control-flow/what-are-callbacks), [promises][promise], and
[async functions](https://jakearchibald.com/2014/es7-async-functions/). For beginners, we recommend promises, although you are free to use whatever format you prefer. If you are unsure, check out our [guide to asynchronous code](/guides/async-code.html).

Most of the API is exposed as:

{% highlight js %}
db.doSomething(args..., [options], [callback])
{% endhighlight %}

… where both the `options` and `callback` are optional.

### Callbacks

Callbacks use the standard Node.js idiom of:

{% highlight js %}
function(error, result) { /* ... */ }
{% endhighlight %}

… where the `error` will be undefined if there's no error.

### Promises

If you don't specify a `callback`, then the API returns a [promise][]. In [supported browsers](http://caniuse.com/#feat=promises) or Node.js, native promises are used, falling back to the minimal library [lie][] as needed.

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**Using Ionic/Angular?**  You can wrap PouchDB promises in [`$q.when()`](https://docs.angularjs.org/api/ng/service/$q#when). This will notify Angular to update the UI when the PouchDB promise has resolved.

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To use a custom promise implementation with PouchDB, you must redefine a global `Promise` object before loading PouchDB:

{% highlight html %}
<script>window.Promise = MyCustomPromiseLibrary;</script>
<script src="path/to/pouchdb.js"></script>
{% endhighlight %}

### Async functions

If you are using a transpiler like [Babel](http://babeljs.io/), you can enable [async functions](https://github.com/tc39/ecmascript-asyncawait), which are an experimental API tentatively slated for release in ES7 (ES2016). This allows you to use the `async`/`await` keywords when consuming promise-based APIs like PouchDB's.

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**How to configure Babel?** To use async functions, you will need the [syntax-async-functions plugin](http://babeljs.io/docs/plugins/syntax-async-functions/), as well as the [transform-regenerator plugin](https://babeljs.io/docs/plugins/transform-regenerator/) or [Kneden](https://github.com/marten-de-vries/kneden) (which is experimental as of this writing). For a full working example, see [async-functions-with-regenerator](https://github.com/nolanlawson/async-functions-with-regenerator).

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Note that the samples for `async`/`await` in the API documentation assume that your code is inside an async function. So for instance:

{% highlight js %}
async function myFunction() {
  // your code goes in here
}
{% endhighlight %}

Any `await` not inside of an async function is a syntax error. For more information about `async`/`await`, read [our introductory blog post](http://pouchdb.com/2015/03/05/taming-the-async-beast-with-es7.html).

[promise]: https://www.promisejs.org/
[lie]: https://github.com/calvinmetcalf/lie
[event emitter]: http://nodejs.org/api/events.html#events_class_events_eventemitter