what does () do at the end of the following code? [duplicate]

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Closed 9 years ago.

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What's the role of the parentheses in the following piece of code?

var dummy = (function (name) {return name;}(dummy || {}));

dummy.foo = ( function(s){
    this.s = s;

    return true;
}) ();

ok so I am not familiar with OO javascript but I know a little bit. Am I correct to say that this is the constructor for foo? what does the () do at the very end? also why is function(s){} in parentesis as well? there was some code in between but I took them out for simplicity sake. Would the above be the same as the below?

dummy.foo = function(s){
    this.s = s;

    return true;
};

I am trying to see what some code someone else wrote does and I don't have much experience in OO side so I am so confused as what's what. I can't even figure out which is the constructor

Answer 1

It's a self-executing JavaScript function:

http://briancrescimanno.com/2009/09/24/how-self-executing-anonymous-functions-work/

Answer 2

var dummy = (function (name) {return name;}(dummy || {}));

This line passes the variable dummy to the function, and returns it exactly; otherwise, it passes an empty object to the function. (The function is evaluated on-the-spot.) The value is then stored in the variable dummy.

dummy.foo = ( function(s){
    this.s = s;

    return true;
}) ();

This defines the property foo to the object dummy. Currently, the function accepts an argument, which is stored to the property s of the object dummy. Currently, because it passes nothing to the function, it stores undefined to the property s.

Answer 3

The parenthesis at the end call the function just defined.

Here foo is a function:

var foo = function (x) { return 2*x; };

Here bar is a number (4 to be precise):

var bar = function (x) { return 2*x; } (2);