js发送按键命令 js在输入框中如何实现回退键功能?

js在输入框中如何实现回退键功能?  

<table id="table_StaticIP" >

<td>IP Address</td>

<td>

<INPUT type=text maxLength=3 size=3 value=0 onkeyup="check(0)" name=ip><b>.</b>

<INPUT type=text maxLength=3 size=3 value=0 onkeyup="check(1)" name=ip><b>.</b>

<INPUT type=text maxLength=3 size=3 value=0 onkeyup="check(2)" name=ip><b>.</b>

<INPUT type=text maxLength=3 size=3 value=0 onkeyup="check(3)" name=ip></td>

</table>

<script type=text/javascript>

var d = document.getElementsByName("ip");

function check(k){

if(k < 0 || k >= d.length)return;

var t = d[k].value.replace(/D/ig, "");

if(t > 255)t = 255;

d[k].value = t;

var e = window.event.keyCode;

if(e == 13 || e == 190 || e == 110){ // 如果输入是回车或者.号 110 - 小键盘 190 - 大键盘 13 - 回车

d[k + 1].focus;

d[k + 1].select;

}

else if(e == 8){ // backspace = 8

if(t == "" && k > 0){

d[k - 1].focus;

move_end(d[k - 1]);

}

}

else{

if(t.length >= 3 && k < d.length - 1){

d[k + 1].focus;

d[k + 1].select;

}

}

}

function move_end(e){ //光标移到最后

var r = e.createTextRange;

r.moveStart('character',e.value.length);

r.collapse(true);

r.select;

}

</script>