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Creating your own bind() (Polyfill of bind)

Uddesh on May 30, 2021

So, what is polyfill? Polyfill is a fallback for a method that is not supported by the browser by default. You can find browser support for any fu...

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Muhammad Hasnain • May 31 '21

Great article, although, I don't think there is any need for this. It is 2021 and support for bind came between 2009 and 2011. Almost all operating systems for all types of devices comes with advanced built-in browsers that supports at least ES6 and almost all of them install and use modern browsers.

Uddesh • May 31 '21

Totally agree, But first of all it helps us to understand how bind() works behind the scene. Apart from that i was asked to implement polyfill of bind() in few interviews as well.

David Matos salvador • Jan 17 '22

this example is to understand how the black box works

Neeraj Sewani • Jan 27 '22

Nice article Uddesh.

Aleksei Berezkin • May 31 '21

Implementing bind with apply is kind of cheating 😉

prashanth • Jan 30 '22

This is a pretty cool post.

I would like to make a small alteration in your code.
We can eliminate the need for storing 'this' in the parent scope and using it at the time by invocation by making use of arrow function.

Function.prototype.myBind = function (obj, ...args) {
  return (...newArgs) => this.apply(obj, [...args, ...newArgs]);
};

Hope this helps!!

Adam Crockett 🌀 • May 30 '21

I haven't used bind very often since arrow functions

Uddesh • May 30 '21

Arrow function are really helpful for adopting ‘this’ from their parent and in most of the use cases we don’t need ‘bind()’, But what if you want ‘this’ to refer to a particular object then you need to use ‘bind()’. I hope you got my point.

Adam Crockett 🌀 • May 31 '21

To be honest, I only use bind for it's less well known second Param. I avoid using this and prefer pure functions, I have very few reasons to make this do anything, bimut that's just me ☺️

Rahul Singh • Jun 12 '23

const module = {
  x: 42,
  getX: function () {
    return this.x;
  },
};

const unboundGetX = module.getX;
console.log(unboundGetX()); // The function gets invoked at the global scope
// Expected output: undefined

const boundGetX = unboundGetX.myBind(module);
console.log(boundGetX());
// Expected output: 42

This myBind does not give the expected output. It gives undefined for both consoles.