Ask HN: JS, what is this called and how does it work? | Hacker News Reader

Ask HN: JS, what is this called and how does it work?

4 pointsuptownhr6 comments

(function(test){console.log(test)})(1)

I don't think this really exists in other languages outside of JS. Where you can send in a parameter this way. I understand that the test variable becomes what ever you pass in the tail end but how does this work? What is this called so I can better ask other JS developers?

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Immediately Invoked Function Expressions (IIFE).

http://benalman.com/news/2010/11/immediately-invoked-functio...

Not unique to js, e.g. upcoming php v7 will support these.

What you have is a self executing anonymous function. Now you know the name you will be able to find out all the information you need. For example: http://esbueno.noahstokes.com/post/77292606977/self-executin...

thank you!

This is the same as:

    var func = (function(test){console.log(test)});
    func(1);

What's going on is you're creating an anonymous function, and then calling it.

So after looking at this longer, it makes a lot more sense. Basically, things are evaluated left to right. The first (function(){}) evaluates the function(){} and returns the function. Then the function is called with the second (1), and passing that in as a param.

That's it. This is often called the module pattern. It's often used to avoid polluting the global scope with variables, e.g.

(function() { var x = 1; console.log(x); })();

console.log(x);

Would output:

undefined

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