Passing Blocks (or Procs) as JS Functions

[richardboehme]

Hey it's me again with another question:

In JS it's common to pass functions as arguments into other functions to provide some type of callback. In Ruby we have a pretty similar approach, but instead of using methods directly we pass in blocks (or procs converted to blocks). Currently it's not possible to pass a block (or proc) to a JS::Object#call function. Something like the following is not possible:

JS::global[:document].call(:addEventListener, 'DOMContentLoaded') do
  puts "Content loaded"
end

In my opinion it would be worth to add this feature. I thought about how it could be implemented and came across an idea of doing it. My idea is to provide a Proc#to_js method that converts the proc into a JS::Object. The JS::Object would be a JS function that holds a reference to the Proc's RbValue object. The function body calls the call function of the Proc to execute it. I implemented this and it seems to be working. However, I do not know yet if it would behave exactly like a normal block would do. Also we would have to figure out what we want to do with block arguments (I guess they could be JS::Objects, maybe primatives could be converted to their Ruby counterparts).

What do you think about this approach? Is there a better way of solving the problem? If you want to I can create a draft PR with my changes to discuss them.

[kateinoigakukun]

@richardboehme This feature looks reasonable to me. PR will be welcomed :)