> For the complete documentation index, see [llms.txt](https://soufatn.gitbook.io/rxjs-book/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://soufatn.gitbook.io/rxjs-book/summary/observable/observable_methods/case.md).

# case

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.