建站常识

<input type='text' id='num' name='tel' value='021jz.com.cn' onKeyUp="showLen(this);">
<span id="span">已输入XX位</span>
<script type="text/javascript">
showLen(document.getElementById("num"));
function showLen(obj){
document.getElementById('span').innerHTML = '已输入'+ (obj.value.length) +'个字符';
}
</script>

JS判断已输入多少字符，提示用户信息