实用的注册表单验证代码

<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>