Example of basic module pattern.

BasicModulePattern.js

var dom = (function() {
    var _counter = 0;
    return {
        generateId : function () {
            return "customId" + _counter++;
        },

        create : function(tagName, id) {
            var el = document.createElement(tagName);
            el.id = id || this.generateId();
            return el;
        }
    }
})();