JavaScriptノード検索方法getElements ByClass Name互換性

var getElementsByClassName = function (opts) {
    var searchClass = opts.searchClass;
    var node = opts.node || document;
    var tag = opts.tag || '*';
    var result = [];
    
    if(document.getElementsByClassName) {
        //      
       var nodes = node.getElementsByClassName(searchClass);
       if(tag !== "*") {
            for(var i = 0; node = nodes[i++];) {
                if(node.tagName === tag.toUpperCase()) {
                    result.push(node);
                }
            }
       } else {
            result = nodes;
       }
    } else {
        //  IE8             
        var els = node.getElementsByTagName(tag);
        var elsLen = els.length;
        var i, j;
        var pattern = new RegExp("(^|\\s)" + searchClass + "(\\s|$)");
        for (i = 0, j = 0; i < elsLen; i++) {
            if(pattern.test(els[i].className)) {
                //        
                result[j] = els[i];
                j++;
            }
        }
    }

    return result;
};