示意图
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<style type="text/css">
.box{
width: 600px;height: 50px;border:2px solid;margin:100px auto;
list-style: none;padding: 0;
display: flex;
}
.box>li{
flex:1;position: relative;
text-align: center;line-height: 50px;
}
.box>li>span{
display:block;
width: 50%;height: 3px;background-color: #000;
position:absolute;
top:70%;left: 50%;
margin-left: -25px;
}
</style>
</head>
<body>
<ul class="box">
<li><span></span></li>
<li><span></span></li>
<li><span></span></li>
<li><span></span></li>
<li><span></span></li>
<li><span></span></li>
</ul>
<script type="text/javascript">
let n = 0;
let lis = document.getElementsByTagName('li');
document.onkeyup = function(e){
e = e || window.event;
key = e.keyCode || e.which || e.charCode;
if( (65<=key&& key<=90) || (48<=key && key<=57) || (96<=key && key<=105) )
{
if(n<=5){
lis[n].innerHTML = e.key;
n++;
}
}
if( key==8 ){
if(n>0){
n--;
let span = document.createElement('span');
lis[n].innerHTML = null;
lis[n].appendChild(span)
}
}
}
</script>
</body>
</html>