Question

I want to know the difference between following javascript functions. Can someone help whats the difference and in what circumstances do we need to use these two functions?

define(function () {

});

the second one is self executing function which is below

(function() { })();

Update

I am using requireJS

Answer 1

Your question title mentions a “jQuery function” but there is no jQuery in the code you’ve shown.

The first bit of code:

define(function () {

});

…calls a function named define and passes an anonymous function as a parameter (some kind of callback?)

The second:

(function() { })();

Defines an anonymous function and calls it immediately.

“whats the difference and in what circumstances do we need to use these two functions?”

Consult the RequireJS API documentation for guidance on when to use the define() function. As for an immediately-invoked-anonymous-function as in your second example there are many different reasons why you might use such a structure, e.g., a common reason is to create working variables and/or nested functions without creating globals.

To my way of thinking comparing the two (without more context, anyway) doesn’t make any more sense than comparing setTimeout(function(){ },1) with (function() { })(); (or comparing any other random function that takes a function as a parameter).