> 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_instance_methods/join.md).

# join

Correlates the elements of two sequences based on overlapping durations.

## Arguments

1. `right` *(`Observable`)*: The right observable sequence to join elements for.
2. `leftDurationSelector` *(`Function`)*: A function to select the duration (expressed as an observable sequence) of each element of the left observable sequence, used to determine overlap.
3. `rightDurationSelector` *(`Function`)*: A function to select the duration (expressed as an observable sequence) of each element of the right observable sequence, used to determine overlap.
4. `resultSelector` *(`Any`)*: A function invoked to compute a result element for any two overlapping elements of the left and right observable sequences. The parameters are as follows:
   1. *(`Any`)* Element from the left source for which the overlap occurs.
   2. *(`Any`)* Element from the right source for which the overlap occurs.

## Returns

*(`Observable`)*: An observable sequence that contains result elements computed from source elements that have an overlapping duration.

## Example