Reactive-Extensions/RxJS

# This is RxJS v 4. [Find the latest version here](https://github.com/reactivex/rxjs)
### `Rx.Observable.prototype.elementAt(index, [defaultValue])`
[Ⓢ](https://github.com/Reactive-Extensions/RxJS/blob/master/src/core/linq/observable/elementat.js "View in source")
 
Returns the element at a specified index in a sequence.  If the specified index is out of bounds and no default value was given `onError` will be called with an error, however, if a default value has been specified, that value will be returned via an `onNext` call.
 
#### Arguments
1. `index` *(`Number`)*: The zero-based index of the element to retrieve.
2. `[defaultValue]` *(`Any`)*: Default value if no such element exists.
 
#### Returns
*(`Observable`)*: An observable sequence that produces the element at the specified position in the source sequence. If the specified index is out of bounds and no default value was given `onError` will be called with an error, however, if a default value has been specified, that value will be returned via an `onNext` call.
 
#### Example
```js
/* Finds an index */
var source = Rx.Observable.from([1,2,3,4])
    .elementAt(1);
 
var subscription = source.subscribe(
  function (x) {
    console.log('Next: %s', x);
  },
  function (err) {
    console.log('Error: %s', err);
  },
  function () {
    console.log('Completed');
  });
 
// => Next: 2
// => Completed
 
/* With default value */
var source = Rx.Observable.from([1,2,3,4])
  .elementAt(4, 42);
 
var subscription = source.subscribe(
  function (x) {
    console.log('Next: %s', x);
  },
  function (err) {
    console.log('Error: %s', err);
  },
  function () {
    console.log('Completed');
  });
 
// => Next: 42
// => Completed
```
### Location
 
File:
- [`/src/core/linq/observable/elementat.js`](https://github.com/Reactive-Extensions/RxJS/blob/master/src/core/linq/observable/elementat.js)
 
Dist:
- [`rx.all.js`](https://github.com/Reactive-Extensions/RxJS/blob/master/dist/rx.all.js)
- [`rx.all.compat.js`](https://github.com/Reactive-Extensions/RxJS/blob/master/dist/rx.all.js)
- [`rx.aggregates.js`](https://github.com/Reactive-Extensions/RxJS/blob/master/dist/rx.aggregates.js)
 
Prerequisites:
- [`rx.js`](https://github.com/Reactive-Extensions/RxJS/blob/master/dist/rx.js) | [`rx.compat.js`](https://github.com/Reactive-Extensions/RxJS/blob/master/dist/rx.compat.js) | [`rx.lite.js`](https://github.com/Reactive-Extensions/RxJS/blob/master/dist/rx.lite.js) | [`rx.lite.compat.js`](https://github.com/Reactive-Extensions/RxJS/blob/master/dist/rx.lite.compat.js)
 
NPM Packages:
- [`rx`](https://www.npmjs.org/package/rx)
 
NuGet Packages:
- [`RxJS-All`](http://www.nuget.org/packages/RxJS-All/)
- [`RxJS-Aggregates`](http://www.nuget.org/packages/RxJS-Aggregates/)
 
Unit Tests:
- [`/tests/observable/elementat.js`](https://github.com/Reactive-Extensions/RxJS/blob/master/tests/observable/elementat.js)