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### `Rx.Observable.case(selector, sources, [elseSource|scheduler])`
[Ⓢ](https://github.com/Reactive-Extensions/RxJS/blob/master/src/core/linq/observable/case.js "View in source")
Uses selector to determine which source in sources to use. There is an alias 'switchCase' for browsers <IE9.
### Arguments
1. `selector` *(`Function`)*: The function which extracts the value for to test in a case statement.
2. `sources` *(`Object`)*: A object which has keys which correspond to the case statement labels.
3. `[elseSource|scheduler]` *(`Observable` | `Scheduler`)*: The observable sequence that will be run if the sources are not matched. If this is not provided, it defaults to `Rx.Observabe.empty` with the specified scheduler.
#### Returns
*(`Observable`)*: An observable sequence which is determined by a case statement.
#### Example
```js
var sources = {
'foo': Rx.Observable.return(42),
'bar': Rx.Observable.return(56)
};
var defaultSource = Rx.Observable.empty();
var source = Rx.Observable.case(
function () {
return 'foo';
},
sources,
defaultSource);
var subscription = source.subscribe(
function (x) {
console.log('Next: ' + x);
},
function (err) {
console.log('Error: ' + err);
},
function () {
console.log('Completed');
});
//=> Next: 42
//=> Completed
```
### Location
File:
- [`/src/core/linq/observable/case.js`](https://github.com/Reactive-Extensions/RxJS/blob/master/src/core/linq/observable/case.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.compat.js)
- [`rx.experimental.js`](https://github.com/Reactive-Extensions/RxJS/blob/master/dist/rx.experimental.js)
Prerequisites:
- If using `rx.expermental.js`
- [`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-Complete`](http://www.nuget.org/packages/RxJS-Complete)
- [`RxJS-Experimental`](http://www.nuget.org/packages/RxJS-Experimental)
Unit Tests:
- [`/tests/observable/case.js`](https://github.com/Reactive-Extensions/RxJS/blob/master/tests/observable/case.js)
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