Javascript - Validation of Email Address

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Email validation with regular expressions is way too much fun. The code that was posted here before is still at the bottom of this page, but I have also added a newer portion. The newer portion requires the passing of the email string instead of the matching of your forms.

-----
- New Version
-----

Remember to pass the email string that you want to validate
when you call this function:

example: validateAddress(document.enter.email.value);

function validateAddress(incoming) {
	var emailstring = incoming;
	var ampIndex = emailstring.indexOf("@");
	var afterAmp = emailstring.substring((ampIndex + 1), emailstring.length);
		// find a dot in the portion of the string after the ampersand only
	var dotIndex = afterAmp.indexOf(".");
		// determine dot position in entire string (not just after amp portion)
	dotIndex = dotIndex + ampIndex + 1;
		// afterAmp will be portion of string from ampersand to dot
	afterAmp = emailstring.substring((ampIndex + 1), dotIndex);
		// afterDot will be portion of string from dot to end of string
	var afterDot = emailstring.substring((dotIndex + 1), emailstring.length);
	var beforeAmp = emailstring.substring(0,(ampIndex));
		//old regex did not allow subdomains and dots in names
		//var email_regex = /^[\w\d\!\#\$\%\&\'\*\+\-\/\=\?\^\_\`\{\|\}\~]+(\.[\w\d\!\#\$\%\&\'\*\+\-\/\=\?\^\_\`\{\|\}\~])*\@(((\w+[\w\d\-]*[\w\d]\.)+(\w+[\w\d\-]*[\w\d]))|((\d{1,3}\.){3}\d{1,3}))$/;
	var email_regex = /^\w(?:\w|-|\.(?!\.|@))*@\w(?:\w|-|\.(?!\.))*\.\w{2,3}/ 
		// index of -1 means "not found"
	if ((emailstring.indexOf("@") != "-1") &&
		(emailstring.length > 5) &&
		(afterAmp.length > 0) &&
		(beforeAmp.length > 1) &&
		(afterDot.length > 1) &&
		(email_regex.test(emailstring)) ) {
		  return true;
	} else {
			alert("Please check your email address!");
			return false;
	}
}

------
- Old Version
------

	<script type="text/javascript" language="javascript">
		<!-- // hide script from old browsers

		// Function to validate email address.
		function validateEmail() {
		   var emailstring = document.enter.email.value;
		   var ampIndex = emailstring.indexOf("@");
		   var afterAmp = emailstring.substring((ampIndex + 1), emailstring.length);
		   // find a dot in the portion of the string after the ampersand only
		   var dotIndex = afterAmp.indexOf(".");
		   // determine dot position in entire string (not just after amp portion)
		   dotIndex = dotIndex + ampIndex + 1;
		   // afterAmp will be portion of string from ampersand to dot
		   afterAmp = emailstring.substring((ampIndex + 1), dotIndex);
		   // afterDot will be portion of string from dot to end of string
		   var afterDot = emailstring.substring((dotIndex + 1), emailstring.length);
		   var beforeAmp = emailstring.substring(0,(ampIndex));
		   var regex = /\;|#|\$|%|\^|&|\*|\(|\)|\+|\\|\/|\?|>|<|\{|\}|\,|\[|\]|\`|\|/;
		   // index of -1 means "not found"
		   if ((emailstring.indexOf("@") != "-1") &&
		      (emailstring.length > 5) &&
		      (afterAmp.length > 0) &&
		      (beforeAmp.length > 1) &&
		      (afterDot.length > 1) &&
		      ! (regex.test(emailstring)) ) {
			  document.enter.submit();
		   } else {
		      alert("Please check your email address!");
		      document.enter.email.focus();
		      return false;
		   }
		}
	//-->
	</script>