Develop rich JavaScript-based user interfaces on Force.com

• Integrate Apex and Visualforce pages with JavaScript libraries
  

Visualforce now lets methods in Apex controllers to be called via JavaScript using the @RemoteAction annotation.

With JavaScript remoting, you can build even more robust functionality in their custom applications.

Code:

@RemoteAction global static String getItemId(String objectName) 

{

 /* ... */

}