Question

I have got a function, inside which are some simple expressions, adding nums, appending doms, etc.
Since I only have to call it once, so an anonymous function could do it. But which way should I choose and what’s the difference?

1: Shorthand for $(document).ready() {}) I seen this a lot,

$(function(){
    var something;
    ++something;
});

2: Found in jquery plugins. Is it binded to $(document).ready() too?

(function ($) {
    var something;
    ++something;
})(jQuery);

Answer 1

The second one is not bound to the ready event.

In detail. This:

$(function(){  /* ... */ });

needs a variable $ defined. Usually this variable exists when jQuery is loaded and points to the jQuery function.

Subsequently, when you call the jQuery function with a function argument, jQuery is binding this function argument to the ready event. The above is equivalent to

jQuery(function(){  /* ... */ });

which is in turn a convenience shorthand for

jQuery(document).ready(function(){  /* ... */ });

---

Your second code snippet

(function ($) { /* ... */ })(jQuery);

does not rely on $ being defined or pointing to jQuery() (this can happen if multiple JS frameworks are loaded in parallel).

To still have the convenience of $ within a certain region of code, it creates a function within which $ is defined and points to jQuery(). However, it is not bound to a DOM event.

But this would be:

(function ($) { 
   $(function(){  /* ... */ });
})(jQuery);

This set-up is used to minimize the conflict between JS frameworks or other pieces of code that rely on $. jQuery plug-in authors use it to write plug-ins that work under many environments.

---

If you think the combined one is too complicated, jQuery also has a shorthand feature, which avoids variable conflicts and binds to document ready at the same time. But be careful, it only works on jQuery and has some downsides.

jQuery(function($) { /* some code that uses $ */ });

For more details, see these two articles:

1. Using jQuery with Other Libraries
2. .ready() @ api.jquery.com (Aliasing the jQuery Namespace)