(source: https://jsfiddle.net/n8w4fggx/7/)

fiddle.js

var OGSend = XMLHttpRequest.prototype.send;

XMLHttpRequest.prototype.send = function(){ 
  console.log("I AM HOOKED!"); 
  return OGSend.apply(this, arguments);
};

var site = 'https://www.google.com';

// vanilla js
var httpRequest = new XMLHttpRequest();
httpRequest.open('GET', site);
httpRequest.send();

// Works with jquery too
$.ajax(site);