Remove events for garbage collector to collect

Is this enough for garbage collector to collect?

const btnEl = document.querySelector('button');

const removeEvent = () => {
     /* Is this enough for garbage collector to collect? */
     btnEl.removeEventListener('click', sayHelloWorld);
};

const sayHelloWorld = () => {
     console.log('Hello world!');

     setTimeout(()=>{
         removeEvent();
     },10000);
};

btnEl .addEventListener('click', sayHelloWorld);

I did some google search and read some stackoverflow answers and one of the answer said something like “if no references pointing to it then the garbage collector will collect it”, I still don’t quite get it, so after I removed the event

btnEl.removeEventListener('click', sayHelloWorld);

do I also need to remove this part of the code?

const sayHelloWorld = () => {
     console.log('Hello world!');

     setTimeout(()=>{
         removeEvent();
     },10000);
};

what does it mean by references pointing to it? Can someone please give me an example code?

Based on my basic understanding…

Yeah, removing the event listener should be sufficient.

what does it mean by references pointing to it?

Garbage collection is automatic and behind the scenes. In some languages you have to do it yourself, but JS does it for you. It keeps checking if there is a reference. What does that mean?

let a = { my: 'data' }; 
a = { new: 'stuff' };

The first line allocates memory for that object and then creates a variable that points to that (reference, pointer, address, whatever you want to call it);

The second line reassigns that variable, it allocates new memory for the new object and overwrites the variable to have the new reference to that. Now nothing is referencing to that old memory location. This is what they are talking about. This is what triggers JS garbage collection.

and for my above code, if I want to fully remove the event and let the garbage collector to collect(release from the memory), this is enough

btnEl.removeEventListener('click', sayHelloWorld);

I don’t need to find a way to remove this too?

const sayHelloWorld = () => {
     console.log('Hello world!');

     setTimeout(()=>{
         removeEvent();
     },10000);
};

Thanks

You’re really working in the wrong language if you want to force memory management decisions. Manual memory management is not what JavaScript is designed for.

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<----- so the garbage collector will collect this part?

Yes, once there is no reference to { my: 'data' }, it will be garbage collected. This is triggered on the second line.

and for my above code, if I want to fully remove the event and let the garbage collector to collect(release from the memory), this is enough

Yes. The reference is being removed behind the scenes and the garbage collection also happens behind the scenes.

It is a good idea to remove event listeners when you don’t need them. Apps that keep recreating event listeners without removing them is a potential source of memory leaks.

I don’t need to find a way to remove this too?

const sayHelloWorld = () => {
   console.log('Hello world!');

    setTimeout(()=>{
       removeEvent();
   },10000);
};

What is the “this” in that sentence? Yes, you need to call removeEvent.

And as Jeremy points out, JS doesn’t let you manage memory, but it does a pretty good job. The issue is to know what to do so it knows to free up the memory - removing unused event handlers is one of them.

Really, I wouldn’t worry about this too much, other than just doing best practices. If you’re curious, you can google “javascript garbage collection” and “javascript memory leaks”. But unless you’re building complex apps and have a memory leak, it usually isn’t something you have to think about.

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yeah, recently I am working on a project that includes alot of adding and removing events and elements and I just want to make sure that the events I removed are fully removed/released from the memory and are collect by the garbage collector so
that I can have an application that is as optimized as possible :slight_smile: :slight_smile:

I mean like after removeEvent() is called

btnEl.removeEventListener('click', sayHelloWorld);

and the event is removed, after the event is removed, should I also remove sayHelloWorld() function too?

let sayHelloWorld = () => {
      /* some code */
};

so maybe something like

sayHelloWorld = '';

or no need to?

We don’t usually worry about removing functions.

The issue isn’t that event listeners (or functions or whatever) take up too much memory. The issue is if these are created dynamically. If I have a section of code with an event listener that keeps getting rendered dynamically, and I never remove any of those event listeners, this will just keep clogging up memory until it crashes.

In the case of a function, you usually aren’t creating them dynamically. I suppose, if you were creating functions on the fly and not clearing out their references, then that could be an issue. I can’t recall ever doing anything like that. Most of the time, your functions are just one instance and not an issue.

I know there is also a case where you can have circular references, like object 1 has a property that references object 2 and object 2 has a property that references object 1, even if you remove the original references, garbage collection can’t get tell that they are not needed. If this is done dynamically, this leads to a memory leak and an eventual crash.

But seriously, unless you are diagnosing a memory leak, I think you’re worrying about this too much. Do some reading if you want out of intellectual curiosity, but don’t worry about it that much. Clearing your event listeners pretty much is all you have to worry about in this case.

So, don’t worry about it so much. Let JS do its thing, remove your event listeners, and don’t worry about memory management unless it becomes a problem.

2 Likes