JS HTTP request interceptor

js_xmlhttprequest_interceptor.js

// Intercept all the HTTP requests and inject a tracker if the payload is JSON
!function() {
  XMLHttpRequest.prototype._original_send = XMLHttpRequest.prototype.send;
  
  let interceptor_send = function(data) {
    try {
      obj = JSON.parse(data);
      obj._tracker = 'tracker_id';
      let new_data = JSON.stringify(obj);
      this._original_send(new_data);
    }
    catch(err) {
      this._original_send(data);
    }
  };
  
  XMLHttpRequest.prototype.send = interceptor_send;
}();