如何验证允许@符号前后的特定点数的电子邮件

Question

var val_em=document.add_indus_detail_form.txt_email.value;
var atpos=val_em.indexOf("@");
var dotpos=val_em.lastIndexOf(".");
if(val_em!='')
{
    if (atpos<1 || dotpos<atpos+2 || dotpos+2>=val_em.length)
      {
      alert("Not a valid e-mail address");
      return false;
      }
    }       

i use this condition to check the email validation that user enters in the textbox how i can validate it like it allows 3 or 4 or any specific numbers of dot allow (ex [e-mail]) before and after the @ but do not allow that dots together (ex: abc@abc...com). also do not allow the spaces in email how it will be have you any idea for this type of validation..

Answer 1

Validations in JavaScript are useless. The user can turn off JS or maybe you encounter a browser who cant even understand JS. This makes your page vulnerable to attacks. So NEVER use JS for validating user inputs.

What you want is RegEx or many if-conditions together with string-functions. My approach: Use a For-Loop, go through the string one by one, check the current character and the one after it. Like this:

for($i = 0; $i < strlen($string); $i++) {
    if(substr($string, 0, 1) == '.' {
        //do something
    }
}