JavaScript makes it easy to validate form fields such as the commonly used email address field.  For web designers trying to validate the email field, this simple script provided by Smart Webby works great.  I thought I'd pass this along, it can be used to easily validate the email field of your contact, comment, etc. forms.  Please let me know what you think or if you're having trouble.

To begin, here's a working example.  Enter an invalid email address and click submit.  You should see a JavaScript alert (the message can be customized).

Demonstration:

 

How to implement in 2 steps:

First Step: Copy and paste this validation JavaScript into the HTML header tags of your page.

<script language = "Javascript">
/**
 * DHTML email validation script. Courtesy of SmartWebby.com (http://www.smartwebby.com/dhtml/)
 */

function echeck(str) {

		var at="@"
		var dot="."
		var lat=str.indexOf(at)
		var lstr=str.length
		var ldot=str.indexOf(dot)
		if (str.indexOf(at)==-1){
		   alert("Invalid E-mail ID")
		   return false
		}

		if (str.indexOf(at)==-1 || str.indexOf(at)==0 || str.indexOf(at)==lstr){
		   alert("Invalid E-mail ID")
		   return false
		}

		if (str.indexOf(dot)==-1 || str.indexOf(dot)==0 || str.indexOf(dot)==lstr){
		    alert("Invalid E-mail ID")
		    return false
		}

		 if (str.indexOf(at,(lat+1))!=-1){
		    alert("Invalid E-mail ID")
		    return false
		 }

		 if (str.substring(lat-1,lat)==dot || str.substring(lat+1,lat+2)==dot){
		    alert("Invalid E-mail ID")
		    return false
		 }

		 if (str.indexOf(dot,(lat+2))==-1){
		    alert("Invalid E-mail ID")
		    return false
		 }
		
		 if (str.indexOf(" ")!=-1){
		    alert("Invalid E-mail ID")
		    return false
		 }

 		 return true					
	}

function ValidateForm(){
	var emailID=document.frmSample.txtEmail
	
	if ((emailID.value==null)||(emailID.value=="")){
		alert("Please Enter your Email ID")
		emailID.focus()
		return false
	}
	if (echeck(emailID.value)==false){
		emailID.value=""
		emailID.focus()
		return false
	}
	return true
 }
</script>

Step Two: Copy and paste the form code or modify yours to work with the code (or visa versa).

<form name="frmSample" method="post" action="#" onSubmit="return ValidateForm()">
                <p>Enter an Email Address : 
                  <input type="text" name="txtEmail">
                </p>
                <p> 
                  <input type="submit" name="Submit" value="Submit">
                </p>
              </form>

Please note: All credit goes to www.smartwebby.com for writing this script. You can view the article here. You can also find a description of the code at that url.