I need to intercept any changes in the content of a cell inside my webpage.

The following code shows me that addEventListener does not work.

function modifyText() {

alert(!);

}



var el=document.getElementById(mycell);

el.innerHTML=a

el.addEventListener(change, modifyText, false); 

// After next instruction I expect an alert message but it does not appear...

el.innerHTML=Z;

The code is just a toy example. In my real case the changes in the page (and therefore in the cell, too) are made by a webapp that I have NO control over.