keyboard Event Listener In JavaScript

Check if this works for you. Your sample line had the a prefix of on which is only used for IEs method attachEvent.

function listener(elem, evnt, func)
{
    if (elem.addEventListener)
        elem.addEventListener(evnt,func,false);
    else if (elem.attachEvent) // For IE
        return elem.attachEvent("on" + evnt, func);
}

listener(document.getElementById('myCanvas'), 'keydown', ev_keydown);