I requested it as a feature here:
its awesome you did it via java script.
If gdevelop had a proper support for shaders (as assets) - like multimedia fusion and construct2 do, I think that it will motivate the community to make and share filters.
Having more filters will empower gdevelop to make more visually impressive games! 
So i really hope to see it added to the trello board, along with some documentation on writing filters/shaders.
Some community shared shaders could even make their way to gdevelop’s git trunk