Unknown javascript function declaration pattern

Question

I have never seen this design pattern before, what is it doing?

(function(def){
    if(typeof module!='undefined'){
        module.exports=def;
    }
    else{
        this.nut=def;
    }
}( function(){
   ...
}() ));

Are you asking why a function is passed to the other function, or how the whole construct (`(function(foo) {...}(bar))`) works? Probably a duplicate of http://stackoverflow.com/questions/592396/what-is-the-purpose-of-a-self-executing-function-in-javascript. — Felix Kling, Aug 08 '12 at 20:25
Seems like an overly complicated way to make a module that falls back to being a global in environments without CommonJS module support. — Esailija, Aug 08 '12 at 20:28
@FelixKling I am asking why, I don't see why you can't just define a function like normal. — Billy Moon, Aug 08 '12 at 20:34

jackwanders · Accepted Answer · 2012-08-08T20:33:10.943

This is a "immediately invoked function expression", as Ben Alman would say. The first function defined takes one argument, def. Wrapping this function in parantheses and passing it a second function definition (also in parentheses) immediately invokes the first function, passing it the result of the second function (it is also immediately invoked) as the def parameter.

More information: http://benalman.com/news/2010/11/immediately-invoked-function-expression/

score 1 · Answer 2 · answered Aug 08 '12 at 20:42

lets decode it step by step

function(def)
{
    if(typeof module!='undefined'){
        module.exports=def;
    }
    else{
        this.nut=def;
    }
}( function(){}());

//the outer brackets removed now as u can see a function is defined which is a normal way to define a function
which takes one argument def
immediately after the definition there is a bracket
so if we breakit down further then

function(def) //function 1
    {
        if(typeof module!='undefined'){
            module.exports=def;
        }
        else{
            this.nut=def;
        }
    }( function() /*function 2*/{}());

this simply means that second function is passed as a parameter to the first function
a bracket () just after the definition of a function in JS signifies that that function here function 1 will be call immediately after the definition. and what ever is inside the brackets will be passed to the function as parameter so def basically is function2

Unknown javascript function declaration pattern

2 Answers2