This extensions will allow you to execute pure GML functions in a separate thread when exporting to HTML5. This means that if you have a script that does a lot of math or causes the game to stutter, this can take some of the load out of the main thread. This done entirely using web worker technology.
This only works with "pure" functions, which means the script can't use anything outside of it. The only variables the script knows about are the arguments passed to it (and the built in ones of course).
Includes fully commented code and an extremely easy to follow example.