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Weak References in JavaScript
ES6 introduced WeakMaps
and WeakSets
, which brings weak and strong references to JavaScript, a concept front-enders are not particularly used to.
If you're working on games, you have to pay very close attention to how memory and performance is managed.
I'm using WeakMap
here as an example, but it's the same for WeakSet
too. The main difference between Map
and Set
is that the latter only keeps unique values.
According to Wikipedia:
In computer programming, a weak reference is a reference that does not protect the referenced object from collection by a garbage collector, unlike a strong reference.
That actually, surprisingly, makes a lot of sense! Wikipedia got me used to definitions like Coroutines are computer program components that generalize subroutines for non-preemptive multitasking by allowing execution to be suspended and resumed
.
Alright, what a WeakMap
does, compared to a good old Map
or {}
is each individual key element in the set can be garbage-collected when they are not referenced somewhere else:
If this is the content of a regular Map
/ {}
:
const bigObject = { id: 'spritesheet-1', data: [ /* gigantic array with a lot of stuff */ ], description: 'hello bla bla',};
And you're only using it in the code like this
const spritesheetID = bigObject.id;// the gigantic array in myMap.data is in memory
The whole object and the gigantic array will remain in memory and will not be CGed until it or its references are destroyed.
Whereas if you use a weak map anything that isn't being used in your program will be garbage-collected.
// create a WeakMap from the big objectconst weakMap = new WeakMap(Object.entries(bigObject));// gigantic array is garbage-collectedconst spritesheetID = weakMap.get('id');
Now you could manually delete
the keys of the object that you don't use, but this trick saves you having to keep track of your usage because this isn't C++.
People have also found other ways to use this with promises and more in this Stackoverflow thread.
That's all for this post! It's a simple concept but needed clarification for me, so I thought I might as well share it.
Cover Photo by Fredy Jacob on Unsplash.
Original Link: https://dev.to/alvinometric/weak-references-in-javascript-3ni9
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