Document.write() - Trap Changes Done To The Document Object

I have been searching for a way to trap changes done to the document object (mainly by the function document.write();).

Example of code that doesn't work:

function myFunction() {
ed.document.onchange = doFunction(document.body.innerHTML);
ed.document.open();
ed.document.write('Hello');
ed.document.close();
}

function do_function(body) {
alert(body);
}

It only fires when the page loads, not when I change the text. You are free to use any event that works, but i think onchange was the one to fit this problem. The alert will write the initialpage, but will never write the tekst 'Hello' that is the new change.

Any javagurus out there know a solution to pick up any fired events triggered by document.write();