fastgame | Optimize system performance for games | Game Engine library

The reason you are getting Uncaught SyntaxError: Unexpected token u in JSON at position 0 is that you are somewhere stuffing undefined into JSON.parse. This is because JSON.parse will convert whatever you passed into it to a string and attempt to parse it, but undefined is not valid JSON, and you are getting an error at the first character already, which is u.

I don't see JSON.parse in your code, so this error must happen in a place you did not copy here.

Everything I'm going to explain below is not going to work unless you fix this error first. So please check where you are parsing your JSON and don't attempt to parse it if the text you are parsing is undefined.

A tip on the side: Open your browser console before the error happens (or refresh the page if you opened it too late). Then you will get more useful error output and most importantly also better info about where the error happened, especially when you have source maps. Even better, you will usually break into the code at the moment the error happens, so you can inspect the variables and see for example why you had undefined there. Also, when you click that file and line number at the right (VM13384:1 in your case), it will show you the line of code where it happened. If the code is minified (which I assume since here it shows line 1), you can click the {} button to auto-format it.

You can use the ternary conditional operator ?:.

The syntax is condition ? valueIfTrue : valueIfFalse, and it evaluates to valueIfTrue when condition was truthy, otherwise it evaluates to valueIfFalse.

For example: