function nextChildNode(node,clazz,tagName){
            var count= node.childElementCount;
            for(var i=0;i<count;i++){
                if(node==undefined || node.children[i]==undefined){
                    continue;
                }
                if(clazz){
                    if(node.children[i].getAttribute('class')==clazz){
                        return node.children[i];
                    }
                }else{
                    if(node.children[i].tagName==tagName){
                        return node.children[i];
                    }
                }


            }
            return null;
        }
        
        function getChildNode(node,classArg,tagNodeArg){
            for(var i=0;i<classArg.length;i++){
                node=nextChildNode(node,classArg[i]);
            }
            for(var i=0;i<tagNodeArg.length;i++){
                node=nextChildNode(node,null,tagNodeArg[i]);
            }
            return node;
        }
        
        function getItemId(node){
            var classNode=['itemInfo','itemDesc'],tagNode=['P','BUTTON'];
            node=getChildNode(node,classNode,tagNode);
            alert(node.getAttribute('itemid'));


        }
        
        #调用函数
        getItemId($(".shopItem")[0]);

JS 遍历子节点查找元素