IE8浏览器是不支持getElementsByClassName

function getElementsByClassName(node, className) {
    if (node.getElementsByClassName) {
        // 使用现有方法
        return node.getElementsByClassName(className);
    } else {
        // 循环遍历所有标签，返回带有相应类名的元素
        var results = [],
            elems = node.getElementsByTagName("*");
        for (var i = 0, len = elems.length; i < len; i++) {
            if (elems[i].className.indexOf(className) != -1) {
                results[results.length] = elems[i];
            }
        }
        return results;
    }
}