Using regular expressions is probably the best way. You can see a bunch of tests here (taken from chromium)

[code]function validateEmail(email) {
var re = /^(([^<>()[]\.,;:s@”]+(.[^<>()[]\.,;:s@”]+)*)|(“.+”))@(([[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}])|(([a-zA-Z-0-9]+.)+[a-zA-Z]{2,}))$/;
return re.test(String(email).toLowerCase());[/code]
}

Here’s the example of regular expresion that accepts unicode:

[code]var re = /^(([^<>()[].,;:s@”]+(.[^<>()[].,;:s@”]+)*)|(“.+”))@(([^<>()[].,;:s@”]+.)+[^<>()[].,;:s@”]{2,})$/i;[/code]

But keep in mind that one should not rely only upon JavaScript validation. JavaScript can easily be disabled. This should be validated on the server side as well.

[code]function validateEmail(email) {
var re = /^(([^<>()[]\.,;:s@”]+(.[^<>()[]\.,;:s@”]+)*)|(“.+”))@(([[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}])|(([a-zA-Z-0-9]+.)+[a-zA-Z]{2,}))$/;
return re.test(email);
}[/code]

[code]
function validate() {
var $result = $(“#result”);
var email = $(“#email”).val();
$result.text(“”);

if (validateEmail(email)) {
$result.text(email + ” is valid :)”);
$result.css(“color”, “green”);
} else {
$result.text(email + ” is not valid :(“);
$result.css(“color”, “red”);
}
return false;
}

$(“#validate”).bind(“click”, validate);[/code]

[code]<script src=”https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js”></script>

<form>
<p>Enter an email address:</p>
<input id=’email’>
<button type=’submit’ id=’validate’>Validate!</button>
</form>

<h2 id=’result’></h2>[/code]