Advanced manipulation of scope in JavaScript

In order to ensure scope-busting for a specific listener in my application, I have implemented the following code:

// within the prototype of MyClass
var self = this;
myElement.addEventListener("stuff", function(e){self.doStuff(e)});

By doing this, I am able to achieve the desired binding for doStuff.

However, an issue arises when attempting to use removeEventListener. It seems that the signatures of the native functions are causing complications.

// within a different prototype of MyClass
var self = this;
myElement.removeEventListener("stuff", function(e){self.doStuff(e)}); // does not work

If I create a separate function that encompasses all of my scope-busting code, the this binding in that code will be unwantedly tied to the object of

myElement</code. Hence, my question is: How can I enforce listener scope while still being able to remove an added event listener?</p>

<p>*Please note that the use of <code>global
or static variables in any way is restricted due to the specific project requirements (otherwise, solving this issue would be straightforward!)

Answer №1

The issue here is not related to scope or how you are storing a reference to this. The problem lies in the fact that removeEventListener requires a reference to a function that was previously registered as a listener, but you are passing a completely new function instead.

To resolve this, you should follow this approach:

var self = this;
var eventHandler = function(e){self.handleEvent(e);}
myElement.addEventListener("event", eventHandler);
// later on
myElement.removeEventListener("event", eventHandler);

Even if the contents of the two functions are identical, they are still considered as distinct functions.

For more information, refer to:

Answer №2

Avoid using inline anonymous functions as it is considered a poor practice. Instead, consider the following more organized approach:

function MyClass() {
    this.onStuff = this.onStuff.bind(this); //Each instance will have a bound version of the prototyped function as their own property
}

MyClass.prototype = {

    onStuff: function (e) { //This function is prototyped but not actually used by any instance
        this.doStuff();
    },

    bind: function () {
        myElement.addEventListener("stuff", this.onStuff);
    },

    unbind: function () {
        myElement.removeEventListener("stuff", this.onStuff);
    }

}

Answer №3

To learn more about removing event listeners from anonymous functions in JavaScript, check out this resource: removeEventListener on anonymous functions in JavaScript

It's important to note that removing event listeners may not be possible when using anonymous functions.

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