console-log-override.js

(function() { 
    var pre = document.createElement('pre');
    document.body.appendChild(pre);
    console = {
        log: function() {
            pre.innerHTML += Array.prototype.slice.call(arguments).map(function(s) { if (s === undefined) return 'undefined'; return s }).join(" ") + "\n";
        }
    }
})()