Refer to url parameters on form load

Refer to url parameters on form load

Greetings

in my app i redirect the user to a certain form and include query parameters in the url: 

openURL("#Form:Ideation?projectId=" + input.ID,"same window");

i want to create a workflow action that would run on form load to use the projectId parameter to fill it in a lookup field. but when i try to refer to it normally (projectId) i get an error saying that projectId is not defined.

what's the correct way to do this in a workflow action deluge code?

Thanks