Question

function sethtml(a,b)
{
    document.getElementById("canvas_html_"+a).
innerHTML = "<iframe frameBorder="0" scrolling="no" width="200" height="40" name='innerFrame'></iframe>";

    var objDoc = window.frames[ "innerFrame" ].document;
    objDoc.write(b);
}

This just adds b to the iframe and the page just gets bigger and bigger.

Answer 1

function sethtml(a,b)
{
    document.getElementById("canvas_html_"+a).src=b;
}

b being a link to new HTML content.

EDIT:

function sethtml(a,b)
{
    var x = document.getElementById("canvas_html_"+a).contentDocument; 
    x.open();
    x.write(b);
    x.close();
}