Javascript Email validator

/
function validate_required(field,alerttxt)
{
with (field)
{
if (value==null||value=="")
{alert(alerttxt);return false}
else {return true}
}
}
function validate_email(field,alerttxt)
{
with (field)
{
apos=value.indexOf("@")
dotpos=value.lastIndexOf(".")
if (apos<1||dotpos-apos<2)
{alert(alerttxt);return false}
else {return true}
}
}
/* International Phone Validator */
// Declaring required variables
var digits = "0123456789";
// non-digit characters which are allowed in phone numbers
var phoneNumberDelimiters = "()- ";
// characters which are allowed in international phone numbers
// (a leading + is OK)
var validWorldPhoneChars = phoneNumberDelimiters + "+";
// Minimum no of digits in an international phone no.
var minDigitsInIPhoneNumber = 10;

function isInteger(s)
{ var i;
for (i = 0; i < s.length; i++)
{
// Check that current character is number.
var c = s.charAt(i);
if (((c < "0") || (c > "9"))) return false;
}
// All characters are numbers.
return true;
}

function stripCharsInBag(s, bag)
{ var i;
var returnString = "";
// Search through string's characters one by one.
// If character is not in bag, append to returnString.
for (i = 0; i < s.length; i++)
{
// Check that current character isn't whitespace.
var c = s.charAt(i);
if (bag.indexOf(c) == -1) returnString += c;
}
return returnString;
}

function checkInternationalPhone(strPhone){
s=stripCharsInBag(strPhone,validWorldPhoneChars);
return (isInteger(s) && s.length >= minDigitsInIPhoneNumber);
}
////////////////////////////////
function validate(thisform)
{
with (thisform)
{
if (validate_required(name,"Please Enter Your Name!")==false)
{name.focus();return false}
else if (validate_required(email,"Please Enter Your Email!")==false)
{email.focus();return false}
else if (validate_email(email,"Invalid Email Address!")==false)
{email.focus();return false}
else if (validate_required(phone,"Please Enter Your Phone Number")==false)
{phone.focus();return false}
else if (checkInternationalPhone(phone.value)==false){
alert("Please Enter a Valid Phone Number")
phone.value=""
phone.focus()
return false
}
else if (validate_required(request,"Please Enter Your Request")==false)
{request.focus();return false}
}
}


In form:-

OnSubmit / OnClick validate(this);