> 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/for.md).

# for | forIn

![for](http://reactivex.io/documentation/operators/images/for.png)

Concatenates the observable sequences or Promises obtained by running the specified result selector for each element in source. There is an alias for this method called `forIn` for browsers \<IE9

## Arguments

1. `sources` *(Array)*: An array of values to turn into an observable sequence.
2. `resultSelector` *(`Function`)*: A function to apply to each item in the sources array to turn it into an observable sequence. The resultSelector is called with the following information: 1. the value of the element 2. the index of the element 3. the Observable object being subscribed
3. `[thisArg]` *(`Any`)*: Object to use as `this` when executing `resultSelector`.

## Returns

*(`Observable`)*: An observable sequence from the concatenated observable sequences or Promises.

## Example