Track down the JavaScript code responsible for polluting the global scope

globals-debugger.js

/**
 * GlobalsDebugger
 *
 * Inspect the stack when a global variable is being set on the window object.
 * Given a global variable name, it proxies the variable name in the window
 * object adding some custom code that will be invoked whenever the variable
 * is set. The custom code will log the current stack trace and halt the code
 * execution to allow inspecting the stack and context in your browser DevTools.
 * You can use the "globalsToInspect" query-parameter to set a comma-separated
 * list of names of the variables you want to inspect.
 * Additionally, you can also add globals to inspect at runtime by invoking
 * "window.__globalsDebugger__.addGlobalToInspect(globalName)" (which will be
 * useful only if you expect these globals to be set asynchronously after you
 * invoked addGlobalsToInspect).
 */
window.__globalsDebugger__ = (function createGlobalsDebugger() {
  // Name of the variables to inspect.
  const globalsToInspect = [];

  // Name of the variables that have already been inspected once.
  const inspectedGlobals = [];

  /**
   * Given a global variable name, halt the code execution when the variable
   * gets set to allow inspecting the stack (to debug what line of code is
   * setting it).
   * @param {string} globalName Name of the global variable to inspect.
   */
  function addGlobalToInspect(globalName) {
    if (!globalsToInspect.includes(globalName)) {
      globalsToInspect.push(globalName);
    }
    // Proxy the global variable that we're interested in to log the stack trace
    // halt the execution when it gets set.
    Object.defineProperty(window, globalName, {
      get: function () {
        return window[`__globals-debugger-proxy-for-${globalName}__`];
      },
      set: function (value) {
        // To avoid noise in case the global is set multiple times, run the 
        // inspection only the first time the variable is set.
        if (!inspectedGlobals.includes(globalName)) {
          inspectedGlobals.push(globalName);
          // Print the stack trace to the console.
          console.trace()
          // Halt the code execution (only if the DevTools are running).
          debugger;
        }
        window[`__globals-debugger-proxy-for-${globalName}__`] = value;
      },
      configurable: true,
    });
  }

  // Start inspecting the global variables listed in the "globalsToInspect"
  // query parameter.
  const parsedUrl = new URL(window.location.href);
  (parsedUrl.searchParams.get("globalsToInspect") || "")
    .split(",")
    .filter(Boolean)
    .forEach((globalToInspect) => addGlobalToInspect(globalToInspect));

  return {
    addGlobalToInspect,
  };
})();