How to find out what's causing my Javascript to crash the browser tab?


I'm making a rather extensive game using Javascript. It is a kind of online game maker that allows players to upload media files and use them to create worlds. Unfortunately, it is rather prone to crashing the browser tab at unpredictable moments. So far, I have found no pattern to this - sometimes it happens within a few minutes, other times it can run for hours without a problem.

I have tried enabling logging in Chrome, but the crashes don't seem to generate an error report in the chrome_debug file.

I thought it might be that the program was using too much memory (given the game's open-ended nature, some worlds can involve downloading rather large data files - though this seems unrelated to when the crash actually happens - while large worlds do seem to be more crash-prone, they do not always crash when the world's data is loaded).

I tried using Electron to turn it into an executable app, but the app still crashes. That shouldn't happen if it's a memory issue, right?

Is there any way of finding out what is causing the code to crash?


Answers:


Most unpredictable crashes in Javascript are caused by memory leaks - objects that are still stored in memory and not being picked up by the garbage collector. Every object in Javascript is stored in a variable somewhere within the global scope, or is associated with another object that is itself connected to the global scope. When a "branch" of the "tree" is removed and can no longer be accessed by the global scope, the garbage collector destroys it.

However, if an object is not being removed from the global scope when it should be, it remains in memory. This usually happens when objects are added to an array but are not removed from that array when they are no longer in use. Over time, these objects build up until the process crashes due to memory overload.

To find memory leaks in Chrome, press F12 and open the Performance tab. By recording the page over time, you can view the amount of memory being used. The green line (nodes) is the most important here - it refers to the number of objects in memory. If nodes are constantly increasing over time (there will always be increases and decreases, but if the overall level is constantly rising) this generally means there's a memory leak.

To find which specific objects are causing the problem, open the Memory tab to take snapshots or timeline profiles of the memory heap. This gives you a count of the specific objects that are in memory at any given time. If there are more of some kind of object than there should be, that's where the leak is.