I have an iframe, it links to an HTML file that has a div that can be edited, I am trying to add content to that div, though all that I have tried hasn't worked.

Here is the iframe:

<div><div id="testing" contenteditable></div></div>

Of course, there is more in the HTML file the iframe displays, but the rest isn't important. So here is the code that I've tried:

function timpin() {
    var iframe = document.getElementById("textField");
    var elmnt = iframe.contentWindow.document.getElementById("testing");
    elmnt.innerHTML += "timpin ";
}

I do believe that it should work, but it isn't and I can't find out why.

I've long forgotten all the web dev things. But i assume to edit an external webpage in an iframe, the only way is to edit the html of said webpage itself (on it's server where it comes from).