JQuery ui.core.js

I found the beginning of the code of ui.core.js of JQuery UI quite interesting,

;jQuery.ui || (function($) {
// code...
})(jQuery);

What is the reason to have ';' in the front?

From stackoverflow

• It is there for concatenation purposes in case one would want to concatenate this file at the end of another script. It effectively fool-proofs concatenation to scripts that have not been terminated properly by a semi-colon.

  So, given the following script:

  alotOfJsCode(argument);
  var fileEnd = noSemiColon
  

  The semi-colon at the beginning allows to prevent this:

  alotOfJsCode(argument);
  var fileEnd = noSemiColonjQuery.ui || (function($) { //...
  

  Which would cause the code to fail.

  In JavaScript, a semi-colon all by itself has no syntactic value. The following two statements are the same:

  //Statement 1
  ;;; ;; ; alert('hello world!'); ;;; ;; ;;
  
  //Statement 2
  alert('hello world!');
  

  musicfreak : Huh, I didn't know that was valid JavaScript. +1