Ajax call too slow ? Javascript and PHP - php

Question

I am setting up a registration form.
This form has 7 fields that are being tested for validation.
2 of them have a special validation; I have an Ajax call to a PHP class where I send an email_string to this class, testing, if such an email already exists in my database (evading duplicates).
params = {};
params['source'] = 'checkEMail';
params['email'] = email
$.ajax({
type: 'POST',
url : 'some_class.php',
data : params,
success: function(msg)
{
if(msg > 0) /* email exists */
is_error = true;
}
});
And in my PHP Class I got something like this:
$final = mysql_fetch_assoc(foo);
echo ($final) ? 1 : 0;
I was testing the data and in fact - I get '1' if the email exists and '0' if it does not.
Funny thing is, that this snippet works fine AS LONG AS there are other errors in this form - like an empty username.
The "is_error" is a boolean that is set to false at the beginning of the script and if one validation fails, it gets true.
Then, finally, I got this:
if(is_error)
{
error.show();
error.empty().append('some html foo');
}
else
{
$('form').submit();
error.empty().hide();
}
So how can it be that I the form will be send although is_error is set to true?
Only reason I could think of is that the form is being send before the "is_error" is being testet - but the send of the form is at the very bottom of the script.
Oh and I am calling it this way:
<script type="text/javascript">
$("#reg_submit").click(function(event) {
event.preventDefault();
checkReg();
});
</script>

Answer 1

instead of having the if(is_error){ part at the end of the script, I would suggest you to do it in the ajax request completion to avoid race conditions:
$.ajax({
type: 'POST',
url: 'some_class.php',
data: params,
success: function(msg) {
if (msg > 0) /* email exists */
is_error = true;
},
complete: function() {
if (is_error) {
error.show();
error.empty().append('some html foo');
} else {
$('form').submit();
error.empty().hide();
}
}
});

Answer 2

Maybe it is caused by different output types that you are trying to match...
First, change your PHP output to
echo json_encode($final ? true : false);
Then, to work with JSON, I would add this line to ajax calling method, to be sure...
$.ajax({
type: 'POST',
dataType:'json',
...
success: function(msg)
{
if(msg!==true){
is_error = true;
}
}
});