Utility Function for Cross-browser Scripting in Vanilla JavaScript

utility.js

/* Utility to add an event listener for an element. */
function addEvent (event, elem, func) {
    if (elem.addEventListener)
        elem.addEventListener(event, func, false);
    else if (elem.attachEvent)
        elem.attachEvent('on'+event, func);
    else
        elem[event] = func;
}

/* Utility to load JavaScript code when the page is ready. */
function loadContent (callback) {
    if (document.addEventListener) {
        document.addEventListener('DOMContentLoaded', function (ev) {
            callback(ev);
        }, false);
    }
    else {
        document.attachEvent('onreadystatechange', function (ev) {
            if ('complete' === document.readyState)
                callback(ev);
        });
    }
}

/* Polyfill of event.preventDefault function. */
if (!Event.prototype.preventDefault) {
    Event.prototype.preventDefault = function () {
        this.returnValue=false;
    };
}

/* console shim for old Internet Explorers */
(function () {
    if ("undefined" === typeof window["console"]) {
        window.console = {
            log: function () {},
            info: function () {},
            warn: function () {},
            debug: function () {},
            error: function () {}
        }
    }
})();