How to Remove Listener from addEventListener Method and on- Event Handler

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addEventListener: Using removeEventListener

First of all:

For the structure of addEventListener, here's the documentation on MDN » API » EventTarget » addEventListener.

For the structure of removeEventListener, here's the documentation on MDN » API » EventTarget » removeEventListener.

Let's use click event for this example.

// The button element. const myButton = document.getElementById("myButton"); // The function being invoked for the click event of an element (button). const clickFunction = (e) => { console.log("CLICK!"); console.log(e); }; // Assign the trigger for the button: addEventListener. const assignClickTrigger = () => { myButton.addEventListener("click", clickFunction); }; // Remove the trigger from the button: removeEventListener. const removeClickTrigger = () => { myButton.removeEventListener("click", clickFunction); }; /* // Now we can use assignClickTrigger and removeClickTrigger. // For activating the listener, we do: assignClickTrigger(); // For DEACTIVATING the listner, we do: removeClickTrigger(); */

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addEventListener with { once: true } Option

With this, we don't need to remove the click listener manually. But that will only be useful if we actually intend to make that element can only be clicked once. Because the listener would be automatically removed when invoked.

The structure goes as such:

myButton.addEventListener("click", clickFunction, { once: true }); // ⬅️ That.

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on- Event

Let's use the similar click event for this example. Thus, it will be onclick.

For the structure of onclick event, here's the reference on MDN » API » Element » click event.

// The button element. const myButton = document.getElementById("myButton"); // The function being invoked for the click event of an element (button). const clickFunction = (e) => { console.log("CLICK!"); console.log(e); }; // Assign the trigger for the button. const assignClickTrigger = () => { myButton.onclick = clickFunction; }; // Remove the trigger from the button. const removeClickTrigger = () => { myButton.onclick = null; /* It can also be: myButton.onclick = ""; // Or: myButton.onclick = undefined; // But, for the intention consistency, to nullify the listener, // it is recommended to reassign using null. */ }; /* // Now we can use assignClickTrigger and removeClickTrigger. // For activating the listener, we do: assignClickTrigger(); // For DEACTIVATING the listner, we do: removeClickTrigger(); */

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Why Do We Need to Remove the Listener?

1. Prevent memory leaks.

   Detached DOM elements with active listeners can consume memory unnecessarily.

2. Improve performance.

   Unused listeners may slow down the application, especially in dynamic or large-scale environments.

3. Avoid unintended behaviour.

   Listeners left active can cause unexpected or duplicate actions, leading to bugs.

4. Clean up resources.

   Removing listeners ensures proper resource management in single-page applications or when reusing components.

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My Issues

I had the issues back then. It was because the elements were dynamically generated, and the event listeners were assigned after the elements were rendered. The assignments kept piling up without proper clean up.

Also, it happened on a static single element. Such as video, or audio element. If the src was dynamically modified and we didn't properly clean up the listener, that would run into unnecessary unpredictabilities.

In conclusion:

by cleaning up listeners when they're no longer needed, we will keep our code efficient and predictable.

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