script tag XHR event listener for monitoring cart activities does not work anymore

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I have an app which will add this script tag into the store.

In the past I use script tag with this script to monitor customer's cart activities.
When the script tag detect a XHR, it will fire some data to my backend.

var oldXHR = window.XMLHttpRequest;

function newXHR() {
  console.log('XHR detected!')
  var realXHR = new oldXHR();
    function () {
      if (realXHR.readyState == 4 && realXHR.status == 200) {
        if (realXHR._url === "/cart.js" || realXHR._url === "/cart/change.js") {
           // do something....
  return realXHR;
window.XMLHttpRequest = newXHR;


But today I don't know why the  action of changing the cart and adding item into cart cannot trigger the XHR listener anymore.
However, this script tag is still working in my old store. But if I install it to a new store, it does not trigger anything. I check the script tag is normally running in that new store, but the problem is the XHR listener did not trigger. 


Anyone have some ideas?