JQuery Validation Plugin: Use remote with delay - php

Question

I am using the remote method from the jQuery validation plugin which makes an ajax call. The remote function is activated each time a key is pressed in the input field. I would like to add a delay, so that the ajax request is only trigged when the user stopped pressing a key for some miliseconds.
This problem was posed in 2012 at GitHub but was closed by the developer in 2015:
I'm sorry for the lack of activity on this issue. Instead of leaving
it open any longer, I decided to close old issues without trying to
address them, to longer give the false impression that it will get
addressed eventually.
In the discussion forum, the user lohfu proposed the following solution:
$.validator.methods._remote = $.validator.methods.remote;
var timer = 0;
$.validator.methods.remote = function () {
clearTimeout(timer);
var args = arguments;
timer = setTimeout(function() {
$.validator.methods._remote.apply(this, args);
}.bind(this), 500);
return "pending";
};
However, there are two main problems:
It does not work. If I add the delay and the remote function returns false, then the form gets still submitted.
When I enter something in the input filed which causes an error by the remote function it correctly gets class="error" assigned. If I now select a different input, the class="error" switches to class="valid", although the error message is still present and the error message is still shown. The same happens when I press submit.
Here is a minimal example:
HTML
<form action="test.php" method= "POST" id="form">
Name: <input type="text" name="name"><br>
Email: <input type="email" name="email"><br>
<input type="submit">
</form>
JS
$("#form").validate({
rules: {
name: "required",
email: {
required: true,
email: true,
remote: {
url: "ajax.php",
type: "post"
}
}
},
messages: {
email: {
remote: "Email already exists"
}
}
});
ajax.php
<?php
header('Content-Type: application/json');
$valid = null;
echo json_encode($valid);
This form should never be submitted, because the ajax.php always returns false. However, entering a name and a valid email will submit the form, despite the fact that the error "Email already exists" is shown.

Answer 1

Does the following fiddle work as expected?
You can change the url into true or false instead:
url: '/echo/js/?js=[null|true|false]',
https://jsfiddle.net/ww0zh9jm/2/
..you have to ad the external resources (Fiddle removes them):
https://ajax.googleapis.com/ajax/libs/jquery/2.2.4/jquery.min.js
https://ajax.aspnetcdn.com/ajax/jquery.validate/1.15.0/jquery.validate.min.js