navigate away alert without saving modifications

I'm developing a website in php.

I want to show a message something like javascript alert, when a user tries to edit or add something in a form and tries to navigate to some other section without saving the modification, i w开发者_运维问答ant to show a message to them,

that you are about to navigate about from this page, your modifications are not saved, do you want to continue?

how can i do this??

any one have an idea ???please share it with me..

Thanks

Use the beforeunload event. Pseudo-code:

window.onbeforeunload = function(e){
   e = e || window.event;
   // check if the user has edited sth
   if(userHasEditedSomething()){
      var msg = "You have unsaved changed. Do you want to navigate away from this page?";
      e.returnValue = msg;
      return msg;
   }
}

Your job is to implement the userHasEditedSomething function that will return true when the user has unsaved changes (filled-in form fields) and false otherwise.

most of the browsers support this event