仿google suggest有问题啊!各路江湖好汉看下啊!

Question

问题如下:
   a)当文本框得到焦点,再按向上键,它从倒数第二个开始(应该从倒数第一开始).
   b)当改变文本框的值后,就没有提示了.
        var maxResult = 7;
        
        var arr1 = new Array("a", "abc", "bdsda", "adsfasdf", "454d21a", "angle", "meiwenhui", "abc", "bdsda", "adsfasdf", "454d21a");
        var arr2 = new Array("s6541fd", "asfdsd", "TWINS", "SHE", "ades", "graseen", "whiste", "resd", "blsue");
        
        
        
        //获的文本框在页面中的绝对坐标
        function getPosition(obj){
            var top = 0, left = 0;
            //直到父容器是body
            do {
                top += obj.offsetTop;
                left += obj.offsetLeft;
            }
            while (obj = obj.offsetParent);
            var arr = new Array();
            arr[0] = top;
            arr[1] = left;
            return arr;
        }
        
        
        //得到文本框的绝对坐标,再创建层主体就非常的方便了.
        function autoComplete(textBox, menuid){
            if (document.getElementById(menuid) == null) {
                var left_new = getPosition(textBox)[1];
                var top_new = getPosition(textBox)[0];
                var newControl = document.createElement("div");
                newControl.id = menuid;
                document.body.appendChild(newControl);
                newControl.style.position = "absolute";
                newControl.style.border = "solid 1px #000000";
                newControl.style.backgroundColor = "#FFFFFF";
                newControl.style.width = textBox.clientWidth + "px";
                newControl.style.left = left_new + "px";
                newControl.style.top = (top_new + textBox.clientHeight + 2) + "px";
                //创建层主体的内容
                newControl.innerHTML = autoCompleteBody(textBox.value);
                // return newControl;
            }
            else {
                //document.getElementById(menuid).innerHTML = autoCompleteBody(textBox.value);
            }
        }
        
        
        function getSearchResult(key){
            switch (key) {
                case "a":
                    return arr1;
                case "s":
                    return arr2;
                default:
                    return new Array();
            }
        }
        
        //生成层主体的内容.
        function autoCompleteBody(key){
            var result = "";
            var j = 0;
            arr = getSearchResult(key);
            
            if (arr.length > maxResult) {
                j = maxResult;
            }
            else {
                j = arr.length;
            }
            for (var i = 0; i < j; i++) {
                result += "<table border='0' cellpadding='2' cellspacing='0' id='menuItem" + (i) + "' onmouseover='forceMenuItem( " + (i) + ");' width='100%' onclick='hide( " + (i) + ")'><tr><td align='left'>" + arr[i] + "</td></tr></table>";
            }
            
            return result;
        }
        
        
        var menuFocusIndex = -1;
        //给选中的数据赋前景色
        function forceMenuItem(index){
            //得到上一次选中的数据项.初始化时没有上一次的选中项
            var lastMenuItem = document.getElementById("menuItem" + menuFocusIndex);
            //上一次不为空
            if (lastMenuItem != null) {
                lastMenuItem.style.backgroundColor = "white";
                lastMenuItem.style.color = "#000000";
                
            }
            
            var menuItem = document.getElementById("menuItem" + index);
            if (menuItem == null) {
                document.getElementById("txt1").focus();
            }
            else {
                menuItem.style.backgroundColor = "cadetblue";
                menuItem.style.color = "#FFFFFF";
                menuFocusIndex = index;
                givNumber(index);
            }
        }
        
        
        /*键盘事件*/
        function catchKeyBoard(){
            var keyNumber = event.keyCode;
            //如果是按的向下
            if (keyNumber == "40") {
                if (menuFocusIndex == maxResult - 1) {
                    forceMenuItem(-1);
                    //当已达到最后一条记录时,将焦点交点文本框
                    menuFocusIndex = -1;
                }
                else {
                    forceMenuItem(menuFocusIndex + 1);
                    givNumber(menuFocusIndex);
                }
            }
            //如果是按的向上 
            if (keyNumber == "38") {
            
                if (menuFocusIndex == -1) {
                    //当已达到第一条记录时且还向上按时,将焦点交点文本框
                    forceMenuItem(maxResult - 1);
                }
                if (menuFocusIndex == 0) {
                    forceMenuItem(menuFocusIndex - 1);
                    menuFocusIndex = -1;
                }
                else {
                    forceMenuItem(menuFocusIndex - 1);
                    givNumber(menuFocusIndex);
                }
            }
            
            
        }
        
        function givNumber(index){
            document.getElementById("txt1").value = arr[index];
            document.getElementById("txt1").focus();
            
        }
        
        function hide(){
            document.getElementById("hui").style.display = "none";
            
        }HTML如下:
     <input type="text" name="txt1" onblur=hide() id="txt1" onkeydown=catchKeyBoard() onKeyUp=autoComplete(this,'hui')>