JS上下左右键在GridView 中移动焦点

var X = 1;
var Y =6;
var rowLen = 0;
var cellLen = 0;
function init() {
var GridView2=document.getElementById ("GridView2");
//GridView2.rows[1].cells[6].all[0].focus();
X = 1;
Y = 6;
rowLen = GridView2.rows.length - 1;
cellLen = GridView2.rows[1].cells.length - 1;
}
document.onkeydown = keyDown;
function keyDown() {
var keycode = event.keyCode;
if ( keycode == 37
|| keycode == 38
|| keycode == 39
|| keycode == 40 ) {
if ( keycode == 37 ) {
if (Y > 6) {
Y--;
}
changeActiveObj(X, Y);
}
if ( keycode == 38 ) {
if (X > 0) {
X--;
}
changeActiveObj(X, Y);
}
if ( keycode == 39 ) {
if (Y < cellLen) {
Y++;
}
changeActiveObj(X, Y);
}
if ( keycode == 40 ) {
if (X < rowLen) {
X++;
}
changeActiveObj(X, Y);
}
}
}
function changeActiveObj(X, Y) {

eval("document.getElementById ('GridView2').rows[" + X + "].cells[" + Y + "].all[0]").focus();
}