What are the Differences Between JavaScript's `call()`, `apply()`, and `bind()` Methods?

Understanding the Distinctions of Javascript's call(), apply(), and bind() Methods

In Javascript, the call() and apply() methods enable developers to specify the context (this) of a function and pass arguments. While both methods serve similar purposes, they differ in how arguments are provided to the function.

When to Use bind()?

The bind() method distinguishes itself from call() and apply() by allowing you to create a new function that preserves the original function's context. This proves valuable when dealing with asynchronous callbacks or events.

Consider the following code snippet:

var obj = {
  x: 81,
  getX: function() {
    return this.x;
  }
};

alert(obj.getX.bind(obj)());
alert(obj.getX.call(obj));
alert(obj.getX.apply(obj));

As the above example demonstrates, bind() returns a new function that, when executed later, maintains the context (this) of the original function. This facilitates the preservation of context in async callbacks and events.

Usage in Events and Asynchronous Callbacks

A common use case for bind() involves event listeners, as seen in the code below:

function MyObject(element) {
    this.elm = element;

    element.addEventListener('click', this.onClick.bind(this), false);
};

MyObject.prototype.onClick = function(e) {
     var t=this;  //do something with [t]...
    //without bind the context of this function wouldn't be a MyObject
    //instance as you would normally expect.
};

In this example, bind() ensures that the onClick() method, when triggered by an event, retains the context of the MyObject instance that initiated the event listener. Without bind(), the onClick() method's context would not be the instance as expected.

An Implementation of bind()

A simplified interpretation of the bind() method can be implemented as follows:

Function.prototype.bind = function(ctx) {
    var fn = this;
    return function() {
        fn.apply(ctx, arguments);
    };
};

This simplified implementation creates a new function that invokes the original function with the provided context (ctx) and arguments. The original Function.prototype.bind() implementation is more complex, handling additional scenarios such as passing additional arguments.

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