Why do jQuery samples often omit script type?

For example here the code goes like this:

<html lang="en">
   <head>
     <!-- whatever -->
     <script>
       $(function() {
         $( "#datepicker" ).datepicker();
       });
     </script>
   </head>
 <!-- whatever -->

Note that <script> should have contained type attribute (perhaps set to "text/javascript") but it is not present here.

This is not the only example I've seen. Such code makes Visual Studio editor unhappy - it underlines <script> and says there should be a type attribute. It also makes me curious big time.

Why is type often omitted? What happens if I add type="text/javascript" - will jQuery break or something?