How to detect if an object has been garbage collected in Javascript?

garbage-collection, javascript

Solution

Normally in JavaScript garbage collection is non deterministic. You cant know if or when an object is garbage collected. This applies to objects that are strong referenced.

In ES12 and after, you can use a `FinalizationRegistry`.

Finalizers lets you handle when an object is garbage collected, using a JavaScript callback. Still the limitation is that, when the callback will get executed is non deterministic. It may take a min or an hour.

// object creation
let abc = new Array(200).fill(true);

const cleanup = new FinalizationRegistry(key => {
  // your code here
});

// tagging variable abc to finalizer
cleanup.register(abc, 'werwer');

// abc = null;

Problem

I am building a JavaScript game that creates a `Level` object using var: ``` function start() { var myGameLevel = new Level(2); } ``` This `Level` object has a lot of functionality, primarily adding elements to the DOM and making them interactive. A simplification: ``` function Level(i) { var _difficulty = i; this.init = function(){ jQuery("#container").append(...game elements here...); jQuery("#button").on('click', function() {...}); } } ``` My question: How can I know if the `Level` object created in the `start` function has been garbage collected or not? I aim to use only `var` variables so that there are no external references. When the DOM is cleared of all game elements, I EXPECT the `Level` object to be released from memory, but how can I be sure?

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