How to retrieve Name from Email Address

You should take note that a valid email address is an incredibly sophisticated object and may contain multiple @ signs (ref. http://cr.yp.to/im/address.html).

"The domain part of an address is everything after the final @."

Thus, you should do something equivalent to:

var email = "[email protected]";
var name = email.substring(0, email.lastIndexOf("@"));

or even shorter,

var name = email.replace(/@[^@]+$/, '');

If you want both the name and the domain/hostname, then this will work:

var email = "[email protected]";
var lasta = email.lastIndexOf('@');
var name, host;
if (lasta != -1) {
    name = email.substring(0, lasta);
    host = email.substring(lasta+1);
    /* automatically extends to end of string when 2nd arg omitted */
} else {
    /* respond to invalid email in some way */
}

var email = "[email protected]";
var name   = email.substring(0, email.lastIndexOf("@"));
var domain = email.substring(email.lastIndexOf("@") +1);

console.log( name );   // john.doe
console.log( domain ); // example.com

The above will also work for valid names containing @ (tools.ietf.org/html/rfc3696^{Page 5}):

john@doe
"john@@".doe
"j@hn".d@e

• String.prototype.substring()
• String.prototype.lastIndexOf()

Using RegExp:

Given the email value is already validated, String.prototype.match() can be than used to retrieve the desired name, domain:

String match:

const name   = email.match(/^.+(?=@)/)[0];    
const domain = email.match(/(?<=.+@)[^@]+$/)[0]; 

Capturing Group:

const name   = email.match(/(.+)@/)[1];    
const domain = email.match(/.+@(.+)/)[1];

To get both fragments in an Array, use String.prototype.split() to split the string at the last @ character:

const [name, domain] = email.split(/(?<=^.+)@(?=[^@]+$)/);
console.log(name, domain);

or simply with /@(?=[^@]*$)/.
Here's an example that uses a reusable function getEmailFragments( String )

const getEmailFragments = (email) => email.split(/@(?=[^@]*$)/);

[ // LIST OF VALID EMAILS:
  `[email protected]`,
  `john@[email protected]`,
  `"john@@"[email protected]`,
  `"j@hn".d@[email protected]`,
]
.forEach(email => {
  const [name, domain] = getEmailFragments(email);
  console.log("DOMAIN: %s NAME: %s ", domain, name);
});