Add New Event to Buttons of default Newform.aspx, Dispform.aspx and Editform.aspx

There comes a situation when you want the default Ok or Edit item or close buttons 
in SharePoint forms pages like Newform.aspx, Dispform.aspx and Editform.aspx to
 redirect user to new page then specified.

To do that we can use java script code to redirect users to different page then the
 normal ones.
I am using an instant of giving an alert to user when user clicks on Ok button of 
editform.aspx .

I am using content editor webpart to add javascript code to editform.aspx page.
You can look into by earlier post if you are not aware of method to put content 
editor webpart in editform.aspx page.

Here is the post click here
After the Webpart is added, make sure the Inside Layout Tab, the Hidden checkmark is
 checked, to hide the webpart during normal use.

In the content editor webpart , put this javascript code:
Replace [] with < >



[script language="javascript" type="text/javascript"]

_spBodyOnLoadFunctionNames.push("StartUpCustomScript");
function StartUpCustomScript() {  
  ChangeOkButtonOnclickEvent("Input","SaveItem");
}
function ChangeOkButtonOnclickEvent(tagName, identifier) {
  var len = identifier.length;
  var tags = document.getElementsByTagName(tagName); 
 /*find all Input type controls on page (ie. control with tag [Input/])*/
  for (var i=0; i < tags.length; i++) {
        var tempString = tags[i].name;       
        if(tempString.indexOf(identifier) == tempString.length-len ) /*find any 
Input type controls on page has its name ending with 'SaveItem'*/
        {
           /*if found, replace it default onclick with our custom script*/

           var func = tags[i].attributes["onclick"].value.replace("if 
(!PreSaveItem())","alert('you have clicked OK');if (!PreSaveItem())");
           /*remove its default onclick event*/
           tags[i].onclick = null;
           /*re-register its onlick event with new script*/
           tags[i].attachEvent("onclick",new Function(func));
       }
    }
    return null;
}  
[/script]




Adding this now as soon as from editform.aspx when you click Ok button , a alert 
message will pop up.



Job done :)