Okay, so I've looked everywhere and can't find a usable answer. I'm on an iMac using p5 and I need to be able to save (by pressing a key, for example) and load (at the start of the program) an integer. If no value is set, make it 0. I don't care what format the integer is saved in, whether it be a text file or any other file type. I've tried using save(), but there's no way to load the contents afterward. Any help?
P5.js doesn't have anything specific for this. You'll have to use regular JavaScript.
You should start a search for "JavaScript save data to file" for a ton of results.
One simple and commonly used option is to use cookies.
To write:
document.cookie = 'value=' + yourValueHere + '; expires=18 Dec 2017 12:00:00 UTC'
Then to read:
var yourValueHere = document.cookie.substring(6);
That's just a very basic example, but hopefully it gets you on the right path. Good luck.