Can you tell me what's the point you want to click this button and not postback?

 

If above funtion, you can simply return true if you want to cancel the postback.

 

 if(command.toLowerCase()=="postback"&&value=="Save")
  {
   alert("The Save Command is Captured at the client side. You can hook up your business logic here.\n You can also stop this command.");
   return true;//return true if you want to stop the command
  }