getElementsByClass代替IE的不兼容性

var getElementsByClass = function (searchClass, node, tag) {
    var classElements = new Array();
    if (node == null)
        node = document;
    if (tag == null)
        tag = '*';
    var els = node.getElementsByTagName(tag);
    var elsLen = els.length;
    var pattern = new RegExp("(^|\\s)" + searchClass + "(\\s|$)");
    for (i = 0, j = 0; i < elsLen; i++) {
        if (pattern.test(els[i].className)) {
            classElements[j] = els[i];
            j++;
        }
    }
    return classElements;
}