Ways to call a function

Consider this simple function:

function my(p) { console.log(p) }

I can call it like this:

my("Hello");

And also like so:

my.call(this, "Hello");

Moreover, this is possible:

Function.prototype.call.call(my, this, "Hello");

A shorthand for the functional way

I am interested in the last option - the most functional one, but since it's too long I tried to make a shorthand:

var call = Function.prototype.call.call;

in order to call my like this:

call(my, this, "Hello");

But I get this TypeError:

TypeError: Function.prototype.call called on inpatible undefined

Anybody knows, what's wrong here?

Ways to call a function

Consider this simple function:

function my(p) { console.log(p) }

I can call it like this:

my("Hello");

And also like so:

my.call(this, "Hello");

Moreover, this is possible:

Function.prototype.call.call(my, this, "Hello");

A shorthand for the functional way

I am interested in the last option - the most functional one, but since it's too long I tried to make a shorthand:

var call = Function.prototype.call.call;

in order to call my like this:

call(my, this, "Hello");

But I get this TypeError:

TypeError: Function.prototype.call called on inpatible undefined

Anybody knows, what's wrong here?

• javascript
• function
• functional-programming

3 Answers 3

When you say

var call = Function.prototype.call.call;

the last call loses its actual context. You need to explicitly say that the call belongs to Function.prototype.call.

You can do that, by creating a new function, which actually binds it like this

var call = Function.prototype.call.call.bind(Function.prototype.call);
call(my, this, "Hello");
// Hello

The bind function returns a new function, which when invoked will have the context (this) set as Function.prototype.call.

call, presumably, makes use of this internally.

By calling it without context, you've changed the internal value of this from something that has access to the function prototype to window.

If you want to do that, then consider this (if you have an ES5 pliant interpreter):

var call = Function.prototype.call.bind(Function.prototype.call)

The bind function makes sure that the context (the this variable) while making the function call is Function.prototype.call instead of undefined, as you see in your case.