Declare a function without a name in JavaScript

Question

I am new to JavaScript (coming from Java) and want to understand this function

(function (global, factory) {
if (typeof define === 'function' && define.amd) {
    define(['../numeral'], factory);
} else if (typeof module === 'object' && module.exports) {
    factory(require('../numeral'));
} else {
    factory(global.numeral);
}

}

It's from this github page https://github.com/adamwdraper/Numeral-js/blob/master/src/formats/currency.js

My question is: Why isn't there a name for the function that takes global and factory as parameter ?

What I would expect is something like this:

function myFunction(p1, p2) {
return p1 * p2;   // The function returns the product of p1 and p2
}

Here, we have the name myFunction but in the above example, we don't have a name for the function. Why? And why is that allowed in JavaScript?

Answer 1

Yes. They are called anonymous functions in Javascript.

Usually these functions are supplied as callbacks to another function.

Or they could be immediately invoked as Jack said in his answer.

Answer 2

It's because it's in an IIFE - you don't need to name the function, and the only real use of naming it would be recursion.

It's like this:

var func = function (global, factory) {
    if (typeof define === 'function' && define.amd) {
        define(['../numeral'], factory);
    } else if (typeof module === 'object' && module.exports) {
        factory(require('../numeral'));
    } else {
        factory(global.numeral);
    }
}

You call it like:

(func)();

Or:

func();

It's a function expression - it doesn't have a name, it's assigned to a named variable. Unnamed functions are known as anonymous functions, and you use them as testing/callback functions.