Next we want to see if the email address the user entered is real. This means that the input data must contain at least an @ sign and a dot (.). Also, the @ must not be the first character of the email address, and the last dot must at least be one character after the @ sign.
At first we check if the user entered anything at all in the email field. Next, we use regular expression and the test() method to check the field for a compliance. Also we will use trim() function that will trim leading whitespace off the string. This won’t be perfect validation — it is possible to slip not compliant addresses by it — but it's normally good enough.
function trim(s)
{
return s.replace(/^\s+|\s+$/, '');
}
function validateEmail(fld) {
var error="";
var tfld = trim(fld.value); // value of field with whitespace trimmed off
var emailFilter = /^[^@]+@[^@.]+\.[^@]*\w\w$/ ;
var illegalChars= /[\(\)\<\>\,\;\:\\\"\[\]]/ ;
if (fld.value == "") {
fld.style.background = 'Yellow';
error = "You didn't enter an email address.\n";
} else if (!emailFilter.test(tfld)) { //test email for illegal characters
fld.style.background = 'Yellow';
error = "Please enter a valid email address.\n";
} else if (fld.value.match(illegalChars)) {
fld.style.background = 'Yellow';
error = "The email address contains illegal characters.\n";
} else {
fld.style.background = 'White';
}
return error;
}
