reactive_ops.when(*dependencies, initial=<Undefined>)[source]#

Returns a reactive expression that emits the contents of this expression only when the dependencies change. If initial value is provided and the dependencies are all param.Event types the expression will not be evaluated until the first event is triggered.

  • dependencies (param.Parameter | rx) – A dependency that will trigger an update in the output.

  • initial (object) – Object that will stand in for the actual value until the first time a param.Event in the dependencies is triggered.