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]);