function checkusername(){
var str=document.getElementById("username").value;
var reg=/^[a-zA-Z]{1}([a-zA-Z0-9]|[._-]){4,19}$/;
if(str.match (reg )==null ){
return false;
}
}function checkall(){
if (checkusername()==false);
{
alert ("用户名错误")
}
}
var str=document.getElementById("username").value;
var reg=/^[a-zA-Z]{1}([a-zA-Z0-9]|[._-]){4,19}$/;
if(str.match (reg )==null ){
return false;
}
}function checkall(){
if (checkusername()==false);
{
alert ("用户名错误")
}
}
<script>
function checkusername(){
var str=document.getElementById("username").value;
var reg=/^[a-zA-Z]{1}([a-zA-Z0-9]|[._-]){4,19}$/;
if(!reg.test(str)){ return false;
}
}function checkall(){
if (checkusername()==false);
{
alert ("用户名错误");
}}
</script>
<input type='text' name='username' onblur='checkall()'>
2.坦白来讲,这里用match是不合适的,应该用test()方法.