What is the meaning of function(){} in javascript?

Question

Recently I came across a piece of code which was like this:

var noop = function(){};
    options.ondragover = options.ondragover || noop;
    options.ondragleave = options.ondragleave || noop;
    options.ondrop = options.ondrop || noop;
    options.onfilesdone = options.onfilesdone || noop;

Answer 1

This is a No Operation function

Discussed in detail in following link

https://disqus.com/home/discussion/chrislaughlin/noop_no_operation_function/oldest/

What is the JavaScript convention for no operation?

Answer 2

The code you posted declared an empty function with the name noop (No Operation) as an alternative to execute when certain conditions apply. For example the code:

options.ondragover = options.ondragover || noop;

checks if options.ondragover exists and if not assigns the empty function to the variable.

Answer 3

It is simply a self executed function in which whatever you declare, you can execute the same.

It restrict the scope and make it private and hide the variables from global objects.

// Somewhere it is defined as global..
var x = 7;  
// Your piece of code
var x = "roman" // Here, you override the value of x defined earlier.
alert(x); // "roman"    
But when you use a closure which you have mentioned:    
var x = 7;   
// it doesn't affect/change the value of global x   
(function (){ var x = "roman";})();
alert(x); // 7