Validasi Email dengan JavaScript

/*
Created by: Anita Sudhakar :: http://www.smartwebby.com/DHTML/email_validation.asp
*/
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("ID Email tidak valid!");
        return false;
    }
    if (str.indexOf(at) == -1 || str.indexOf(at) == 0 || str.indexOf(at) == lstr) {
        alert("ID Email tidak valid!");
        return false;
    }
    if (str.indexOf(dot) == -1 || str.indexOf(dot) == 0 || str.indexOf(dot) == lstr) {
        alert("ID Email tidak valid!");
        return false;
    }
    if (str.indexOf(at, (lat + 1)) != -1) {
        alert("ID Email tidak valid!");
        return false;
    }
    if (str.substring(lat - 1, lat) == dot || str.substring(lat + 1, lat + 2) == dot) {
        alert("ID Email tidak valid!");
        return false;
    }
    if (str.indexOf(dot, (lat + 2)) == -1) {
        alert("ID Email tidak valid!");
        return false;
    }
    if (str.indexOf(" ") != -1) {
        alert("ID Email tidak valid!");
        return false;
    }
    return true;
}

function ValidateForm() {
    var emailID = document.frmSample.txtEmail;

    if ((emailID.value == null) || (emailID.value == "")) {
        alert("Ketik alamat email Anda!");
        emailID.focus();
        return false;
    }
    if (echeck(emailID.value) == false) {
        emailID.value = "";
        emailID.focus();
        return false;
    }
    return true;
}

<form name='frmSample' method='post' action='#' onSubmit='return ValidateForm()'>
Masukkan alamat email: 
    <input type='text' name='txtEmail' /> 
    <input type='submit' name='submit' value='Submit' />
</form>

Lihat Demo

Pembaharuan

Filter yang lebih sederhana dengan regex dari Dynamic Drive:

/*
 * Email Validation script- © Dynamic Drive (www.dynamicdrive.com)
 * This notice must stay intact for legal use.
 * Visit http://www.dynamicdrive.com/ for full source code
 */

var emailfilter = /^\w+[\+\.\w\-]*@([\w\-]+\.)*\w+[\w\-]*\.([a-z]{2,4}|\d+)$/ig;

function checkmail(e) {
    var checkval = emailfilter.test(e.value);
    if (checkval == false) {
        alert("ID Email tidak valid!");
        e.select();
    }
    return checkval;
}

<form name='taufik'>
    <input name='prikitiwform' type='text' />
    <input type='submit' onClick='return checkmail(this.form.prikitiwform)' value='Submit' />
</form>

Lihat Demo