Nested if statement not firing - php

Question

I am posting data to my db, however, before I do I have set in my php to echo out any issues. When the 'data != 'signup success' it should run the if within it, this does not work. Any ideas ?
PHP:
if($u == ""){
echo "Please create a username";
exit();
}
Js:
var submitBtn = $('#signUpBtn');
submitBtn.on('click', function() {
var fn = $('#fname'),
ln = $('#lname'),
u = $('#uname'),
e = $('#email'),
p = $('#pword1'),
p2 = $('#pword2'),
fnVal = fn.val(),
lnVal = ln.val(),
uVal = u.val(),
eVal = e.val(),
pVal = p.val(),
p2Val = p2.val();
$.post('phpsrc/parsers/signUp.php',
{fn: fnVal, ln: lnVal, u: uVal, e: eVal, p: pVal},
function(data) {
if (data != 'signup success') {
if (data === 'Please create a username') {
alert('uname');
}
} else {
}
}
);
});

Answer 1

You'd be better off json encoding the data:
if($u == ""){
$data = array("response" => "Please create a username");
exit(json_encode($data));
}
Allowing you to check the response in your ajax request like this:
function(data) {
if (data.response !== 'signup success') {
if (data.response == 'Please create a username') {
alert('uname');
}
} else {
alert('something');
}
}