Why use Function.prototype.bind instead of Function.prototype.call?

Question

myFunction.call(thisArg, arg1, arg2 ...)

My understanding is that when I use call method and provide a thisArg the this value in the function is set to object I pass in.

myFunction.bind(thisArg, arg1, arg2 ...)

And the bind method on the other hand returns a new function with the context of this of the new function set to the object I pass in.

But what I don't understand is why use bind instead of a call. If all I want to do is change the context of this, call seems sufficient to me. Then why use bind when it breaks in browsers IE8 and below.

So, when does using bind become a better case compared to call?

When you want to pass the bound function to something else.

Paul Grime
– Paul Grime

2013-04-06 20:18:31 +00:00
Commented Apr 6, 2013 at 20:18 — Paul Grime
– Paul Grime, Commented Apr 6, 2013 at 20:18

zzzzBov · Accepted Answer · 2013-04-06 20:24:19Z

12

When does using bind become a better case compared to call?

Callbacks.

If you need to make sure that a function is called in the context of a particular object, but have no controll of how the function is called (such as when you pass a function as a parameter to a callback), you'd use bind.

var f,
    example;
f = new Foo();
example = document.getElementById('example');

//`f.bar` is called in the context of `f`
f.bar();

//`f.bar` will be called in the context of `example`
example.addEventListener('click', f.bar); 

//`f.bar` will be called in the context of `f`
example.addEventListener('click', f.bar.bind(f));

edited Apr 6, 2013 at 20:24

answered Apr 6, 2013 at 20:19

zzzzBov

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1 Comment

nimgrg Over a year ago

Was very nooby of me, but creating this fiddle based on your example helped me clear the idea. Thanks!!

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