depends on the game engine. tits have a custom engine that exposes it's variables in a global scope, you just have to type `window` in your browser's devtools, and look over the entries in resulting object. harlowe doesn't expose it's internals by default, but that can be changed by adding a couple of lines to it's script area to bump them into the window scope, google will serve you better with the details. tweego can be used to decompile and recompile twine games, and node-js packages like js-beautify and webcrack can assist with making sense of other html games.
also, thank you for not using save editors. they often introduce issues that can be a bitch to try and debug when an idiot user reports them, not understanding that their broken game is their own doing. sure, devtools can break a game as well, but at least there's way less perceived conviction that "save editing is safe to do and no way it's the cause of any issues"