JavaScript简单验证表单空值及邮箱格式的方法

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta http-equiv="Content-Language" content="zh-cn" />
<title>Javascript 表单验证</title>
<body>
 <h3>（一）验证必填项是否有空值。</h3>
 <form action = "submitpage.html" onsubmit = "return validate_form(this)" method = "post">
 Name:<input type = "text" name = "name" size = "20">
 <input type = "submit" value = "Submit">
 </form>
 <h3>（二）验证Email格式是否正确。</h3>
 <form action = "submitpage.html" onsubmit = "return is_email_form(this)" method = "post">
 Email:<input type = "text" name = "email" size = "20">
 <input type = "submit" value = "OK">
 </form>
 <script>
//判断内容是否为空
 function validate_form(thisform){
  with (thisform){
   if (!validate_required(name,"Name must be filled out!")){
    name.focus();
    return false
   }
  }
 }
 function validate_required(field,alerttxt){
   with (field){
    if (value==null||value==""){
     alert(alerttxt);
     return false
    }else {
     return true
    }
   }
  }
//判断内容是否符合email的格式
function is_email_form(thisform){
 with(thisform){
  if(!checkEmail(email,"Not a valid e-mail address!")){
   email.focus();
   return false;
  }
 }
}
function checkEmail(field, alertText){
 with(field){
  apos = value.indexOf("@");
  dotPos = value.indexOf(".");
  if(apos<1 || dotPos-apos<2){
   alert(alertText);
   return false;
  }else{
   return true;
  }
 }
}
 </script>
</body>
</html>