getElementsByClassName方法的封装

Element.prototype.getElementsByClassName = function(searchClass,node,tag){
    if(document.getElementsByClassName){
         var nodes = (node || document).getElementsByClassName(searchClass);
         var result = [];
         for(var i = 0;node = nodes[i++];){
              if(tag !== "*" && node.tagName === tag.toUpperCase()){
                   result.push(node);
              }
        }
        return result;  
    }else{
        node = mode || document;
        tag = tag || "*";
        var classes = searchClass.split("");
        var elements = (tag === "*" && node.all) ? node.all : node.getElmentsByClassName(tag);
        var patterns = [];
        var current;
        var match;
        var i = classes.length;
        while(--i >= 0){
              patterns.push(new RegExp("(^|\s)" + classes[i] + "(\s|$)"));
        }
        var j = elements.length;
        while(--j >= 0){
              current = elements[j];
              match = false;
              for(var k = 0,kl = patterns.length;k < kl;k++){
                match = patterns[k].test(current.className);
                if(!match){
                      break;
                }
            }
            if(match){
                result.push(current);
            } 
        }
        return result;
    }      
}