Explain the following JavaScript statement?

This question already has an answer here:

How do JavaScript closures work? 88 answers

Why do you need to invoke an anonymous function on the same line? 19 answers

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This code is equivalent to:

function Ninja() {
    // nothing here
}

var ninja = new Ninja();

Though in the code you listed, the function/object Ninja is not global scope.

The code (function() {...})(); basically says "take whatever function is contained inside here and execute it immediately". So it's creating an anonymous function and calling it right afterwards.

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It's called an Immediately-Invoked Function Expression (or IIFE). It creates a new scope and executes the contents immediately. There are many uses for it; the one I use the most is when the this keyword would change meaning, eg in

var someClass = function() {
    this.property = something;
    this.update = (function(obj) {
        function() {
            $('.el').each(function() {
                $(this).html( obj.property );
            });
        };
    )(this);
};

While I want to refer to this.property inside the $('.el').each() , this changes meaning within that scope and refers to the current DOM element that is being looped through with .each() . So by passing this as a parameter into the IIFE (and calling that parameter obj ) I can use obj.property to refer to what is this.property when outside the scope of $('.el').each( ..., function() { ... }); .

Let me know if that makes sense or if you have any questions :)

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Why is the function declaration encapsulated in '('s and also why is there a '();' in the end

Its declaring and executing the function at the same time.

You may see: Named function expressions demystified - by Juriy "kangax" Zaytsev

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