Validating email is a very important point while validating an HTML form. In this page we have discussed how to validate an email using JavaScript :

An email is a string (a subset of ASCII characters) separated into two parts by @ symbol. a “personal_info” and a domain, that is personal_info@domain. The length of the personal_info part may be up to 64 characters long and domain name may be up to 253 characters

The personal_info part contains the following ASCII characters.

Uppercase (A-Z) and lowercase (a-z) English letters.
Digits (0-9).
Characters ! # $ % & ' * + - / = ? ^ _ ` { | } ~
Character . ( period, dot or fullstop) provided that it is not the first or last character and it will not come one after the other.
The domain name [for example com, org, net, in, us, info] part contains letters, digits, hyphens, and dots.

Example of valid email id

mysite@ourearth.com
my.ownsite@ourearth.org
mysite@you.me.net

Example of invalid email id

mysite.ourearth.com [@ is not present] 
mysite@.com.my [ tld (Top Level domain) can not start with dot "." ]
@you.me.net [ No character before @ ]
mysite123@gmail.b [ ".b" is not a valid tld ]
mysite@.org.org [ tld can not start with dot "." ]
.mysite@mysite.org [ an email should not be start with "." ]
mysite()*@gmail.com [ here the regular expression only allows character, digit, underscore, and dash ]
mysite..1234@yahoo.com [double dots are not allowed]

function ValidateEmail(mail) 
{
 if (/^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/.test(myForm.emailAddr.value))
  {
    return (true)
  }
    alert("You have entered an invalid email address!")
    return (false)
}