I'm embedding GMStudio game in browser using . I need to send some data to the game from site's frontend in JSON and to receive some data from the game in frontend to make consequent actions.
So, my idea before was to save data in cookies/localStorage and to get it in the game somehow, using HTTP functionality or DLL's. Also, I'd like to emit messages from the game using window.parent.postMessage and receive them in frontend correctly.
Alas, I did not find a way to implement this. I hope there's some consistent approach to this problem about which I do not know.
The backup plan is to use Game Maker http_post_string and web sockets to get user's data before game's start and to make frontend do something after game's ending. It's clumsy and insecure, however.
The standard approach is to make a JavaScript extension.
That is done by creating a blank extension, adding a blank JS file to it, defining the functions via the context menu on it, and then adding the implementations into the JS file. Then you'll be able to call them from GML side as per usual.
This way you can access LocalStorage\Cookies, transmit\receive data from JS backends, and overall mess with the runtime as you please (with various degrees of understanding required to access internal data).