javaScript 简单验证代码（用户名，密码，邮箱)

<script language="javascript"> 
function IsDigit(cCheck) 
{ 
return (('0'<=cCheck) && (cCheck<='9')); 
} 
function IsAlpha(cCheck) 
{ 
return ((('a'<=cCheck) && (cCheck<='z')) || (('A'<=cCheck) && (cCheck<='Z'))) 
} 
function IsaNull(cCheck) 
{ 
return(cCheck != " ") 
} 
function checkform() 
{ 
id = document.sform1.id.value; 
if (id == "") 
{ 
alert("请输入注册名"); 
document.sform1.id.focus(); 
return false; 
} 
for (nIndex=0; nIndex<id.length; nIndex++) 
{ 
cCheck = id.charAt(nIndex); 
if (!(IsDigit(cCheck) || IsAlpha(cCheck) || cCheck=='-' || cCheck=='_' || cCheck=='.')) 
{ 
alert("用户名只能使用字母、数字以及-、_和.，并且不能使用中文"); 
document.sform1.id.focus(); 
return false; 
} 
} 
chineseid = document.sform1.chineseid.value; 
if (chineseid == "") 
{ 
alert("请输入中文昵称"); 
document.sform1.chineseid.focus(); 
return false; 
} 
password = document.sform1.password.value; 
if (password == "") 
{ 
alert("请输入登陆密码"); 
document.sform1.password.focus(); 
return false; 
} 
password1 = document.sform1.password1.value; 
if (password>password1) 
{ 
alert("重复密码与登陆密码不相同"); 
document.sform1.password.focus(); 
document.sform1.password1.focus(); 
return false; 
} 
if (password<password1) 
{ 
alert("重复密码与登陆密码不相同"); 
document.sform1.password.focus(); 
document.sform1.password1.focus(); 
return false; 
} 
if (document.sform1.email.value == "") 
{ 
alert("请输入您的E-MAIL地址"); 
document.sform1.email.focus(); 
return false; 
} 
email=document.sform1.email.value; 
emailerr=0 
for (i=0; i<email.length; i++) 
{ 
if ((email.charAt(i) == "@") & (email.length > 5)) 
{ 
emailerr=emailerr+1 
} 
} 
if (emailerr != 1) 
{ 
alert("请输入正确的E-MAIL地址"); 
document.sform1.email.focus(); 
return false; 
} 
if (document.sform1.checkask.value=="") 
{ 
alert("密码提示问题不能为空"); 
document.sform1.checkask.focus(); 
return false; 
} 
if (document.sform1.checkans.value=="") 
{ 
alert("您的密码提示问题答案不能为空"); 
document.sform1.checkans.focus(); 
return false; 
} 
return true; 
} 
</script>