Is this jQuery related, and what does this mean? [duplicate]

Question

I have been searching, but no clues... or I haven't search the proper way (so please excuse me if duplicate)

Does the following code, mean: If there is no jQuery defined, or no document ready?

!function ($) {

///

!function ($) {

  $(function(){ // I know this is an alias to $(document).ready()

  .....

}(window.jQuery) // Ending of !function

I'm asking, because I saw it here: http://twitter.github.io/bootstrap/assets/js/application.js and have no I really don't know what it means.

Answer 1

In this case, ! is being used because it's an operator, so the rest of the line will be treated as an expression rather than a statement. This is a way of writing an immediately invoked function expression. The more common idioms can be found here:

Javascript immediately invoked function patterns

Answer 2

! on a function(){}() simply flips (or negates) the value that's returned after immediately calling the function that's defined. Notice that immediately after the function definition, at the very last line, it says (window.jQuery) — that's passing jQuery as the argument to the function and calling it immediately.

But in this case it doesn't appear to do anything important since the return value won't be used anyway. The function will still be executed though.

Also, it says this at the top of the file:

// NOTICE!! DO NOT USE ANY OF THIS JAVASCRIPT
// IT'S ALL JUST JUNK FOR OUR DOCS!
// ++++++++++++++++++++++++++++++++++++++++++

So that's evidence further that it's not meant to serve any real purpose.