实现ES5以下兼容，Object.create()、getElementsByClassName()

Object.create：
搞清楚new F()和Object.create(F.prototype)是一样的

if (!Object.create) {
    Object.create = function(proto) {
        function F() {};
        F.prototype = proto;
        return new F;
    }
}

getElementsByClassName：

function getByClass(clsName, parent) {
    var oParent = parent ? document.getElementById(parent) : document,
        eles[],
        elements = oParent.getElementsByTagName('*');

    for (var i = 0, l = elements.length; i < l; i++) {
        if (elements[i].className.match(new RegExp('(\\s|^)' + clsName + '(\\s|$)'))) {
            eles.push(elements[i]);
        }
    }
    return eles;
}