Link PHP with Ajax Magento 2 - php

Question

I'm trying to create a simple "Register your interest" action. I have the front end working but I'm not sure how to link the AJAX to the PHP file. Where do I put the PHP file?
My current code for the AJAX is:
$.ajax({
url: "register-interest.php",
type: "GET",
dataType: "json",
data: {
type : "registerInterest",
email : userEmailLog,
user : userNameLog,
product : productTitle,
sku : productSku
},
success: function (response) {
JSON.stringify(response);
},
error: function (err) {
JSON.stringify(err);
},
complete : function() {
//$('.user-accept').addClass('unhide');
loading();
}
});

Answer 1

First you check url variable is correct or not and then provide response any data like
success: function (response) {
JSON.stringify(response);
},

Answer 2

Your url value is:
"register-interest.php"
This implies that the php file that processes the AJAX request needs to be available at the same directory level as the page that includes the javascript file that is performing the AJAX request.
Example:
If your page is at http://example.com/my/ajax/page.html
Then the javascript will perform the AJAX request to the URL http://example.com/my/ajax/register-interest.php
Alternatively if you change the JS url value to read "/register-interest.php", then the AJAX request will be made to: http://example.com/register-interest.php
Where you need to put it on your server depends on how your web server's webroot's folder structure is organised, but you should be able to work back from the URL the javascript will be requesting to work this out.