Question

What is the difference between the following function definitions?

1:

$(function () {
    //stuff here
}); 

2:

function($){
    //stuff here
}

Answer 1

In #1, your function will be called by jQuery when the DOM is ready; passing a function into $() is a shortcut for $(document).ready(function() { ... }); (details here).

In #2, you’re defining a function but neither calling it nor asking jQuery to call it. (And in fact, as shown, it’s a syntax error — you’d need to be assigning it to something or calling it for it to be valid without a name.) Nothing you’ve quoted will execute the function, you’d have to call it yourself.

On #2, the idiom you’ve probably seen there is:

(function($) {
    // ...code using `$` for jQuery here...
})(jQuery);

That’s fairly standard thing you’d do when you want the code to run immediately (not wait for DOM ready), and you want to use $ within the function to refer to jQuery, but you want to be compatible with noConflict mode. You see this a lot in plug-ins. It defines a function accepting a $ argument, which shadows any $ defined globally, and then immediately calls that function passing in jQuery as the argument. So even if $ doesn’t map to jQuery globally, it does within that function. You can do the same thing like this:

(function() {
    var $ = jQuery;
    // ...code using `$` for jQuery here...
})();

…but for some reason the earlier example is more common, even if a bit less clear. (It’s a couple of characters shorter, I suppose.)