JQuery

JQuery is a JavaScript library that works across all browsers.
It makes things like HTML document traversal and manipulation, event handling and AJAX much easier.
The library takes common tasks and wraps them into small reusable methods.

$ is shorthand for jQuery

<script src="https://code.jquery.com/jquery-1.10.2.js"></script> 
<script src="https://code.jquery.com/jquery-1.9.1.js"></script>

<html> 
<head> 
  <script src="https://code.jquery.com/jquery-1.10.2.js"></script> 
  <script> 
   jQuery(document).ready(function() { 
      jQuery("p").text("The DOM is ready");  //all paragraph elements in the DOM 
   }); 
   </script> 
</head> 
<body> 
   <p>Not Loaded</p> 
</body> 
</html>

DOM, AJAX, Events, Effects
jquery.com

Refers to a specific DOM element

#("#myid")

jQuery.myCustomMethod = function() { alert("hello"); };