代码如下：
<!doctype html> <html> <head> <meta charset="utf-8"> <title>telephone number</title> <style> *{ margin:0; padding:0; } form{ width:300px; position:relative; margin:10px; } fieldset{ padding:10px; border:1px dashed #ddd; } #num_info{ display:none; position:absolute; left: 11px; bottom: 37px; width: 170px; height:30px; border:1px solid #ddd; border-bottom:none; background-color:#f6f6f6; font:20px/30px verdana,arial; color:#F90; } #num{ width:170px; height:24px; line-height:24px; margin-top:40px; border:1px solid #bbb; } #num:focus{ outline:none; border-color:#999; } p{ font-size:12px; color:#999; } </style> </head> <body> <form> <fieldset> <label for="num"></label> <input type="text" maxlength="11"> </fieldset> </form> <script> window.onload=function(){ var $numInfo=document.getElementById('num_info'), $num=document.getElementById('num'), _val,_val1,_val2; $num.onkeyup=function(){ var val=this.value=this.value.replace(/[^\d]/g,''), len=val.length; if(val!=''){$numInfo.style.display='block';} if(len<=3){ _val=_val1= val.substr(0,3); } else if(len>3&&len<=7){ _val=_val2=_val1+"-"+val.substr(3,len); } else if(len>7){ _val=_val2+'-'+val.substr(7,len); } $numInfo.innerHTML=_val; } $num.onblur=function(){ $numInfo.style.display='none'; } } </script> </body> </html>