What are Deffered Scripts in Java Scripts

                 What's  are the problem with normal scripts ?

• Browser must halt parsing the html until the scripts is downloaded  and executed (since the script might call document.write(...) or define global variable that are later scripts depend on ) 
• Any images and style sheets that follow the script tag don't start downloading and executing. 

       A defer  external Scripts will start downloading immediately but won't execute until after the                   page is rendered.

       After the page has rendered , all defer scripts are executed in the same order that they were         declared. Not all browser implement defer the same way .

       The purpose of defer is to indicate that a script won't changing the structre of the page as it         executes