JAVASCRIPT iframe.contentWindow.js

log("loading iframe.contentWindow.js");

try {
  // Adds a contentWindow proxy to the provided iframe element
  const addContentWindowProxy = (iframe) => {
    const contentWindowProxy = {
      get(target, key) {
        // Now to the interesting part:
        // We actually make this thing behave like a regular iframe window,
        // by intercepting calls to e.g. `.self` and redirect it to the correct thing. :)
        // That makes it possible for these assertions to be correct:
        // iframe.contentWindow.self === window.top // must be false
        if (key === "self") {
          return this;
        }
        // iframe.contentWindow.frameElement === iframe // must be true
        if (key === "frameElement") {
          return iframe;
        }
        return Reflect.get(target, key);
      }
    };

    if (!iframe.contentWindow) {
      const proxy = new Proxy(window, contentWindowProxy);
      Object.defineProperty(iframe, "contentWindow", {
        get() {
          return proxy;
        },
        set(newValue) {
          return newValue; // contentWindow is immutable
        },
        enumerable: true,
        configurable: false
      });
    }
  };

  // Handles iframe element creation, augments `srcdoc` property so we can intercept further
  const handleIframeCreation = (target, thisArg, args) => {
    const iframe = target.apply(thisArg, args);

    // We need to keep the originals around
    const _iframe = iframe;
    const _srcdoc = _iframe.srcdoc;

    // Add hook for the srcdoc property
    // We need to be very surgical here to not break other iframes by accident
    Object.defineProperty(iframe, "srcdoc", {
      configurable: true, // Important, so we can reset this later
      get: function() {
        return _iframe.srcdoc;
      },
      set: function(newValue) {
        addContentWindowProxy(this);
        // Reset property, the hook is only needed once
        Object.defineProperty(iframe, "srcdoc", {
          configurable: false,
          writable: false,
          value: _srcdoc
        });
        _iframe.srcdoc = newValue;
      }
    });
    return iframe;
  };

  // Adds a hook to intercept iframe creation events
  const addIframeCreationSniffer = () => {
    /* global document */
    const createElementHandler = {
      // Make toString() native
      get(target, key) {
        return Reflect.get(target, key);
      },
      apply: function(target, thisArg, args) {
        const isIframe = args && args.length && `${args[0]}`.toLowerCase() ===
          "iframe";
        if (!isIframe) {
          // Everything as usual
          return target.apply(thisArg, args);
        } else {
          return handleIframeCreation(target, thisArg, args);
        }
      }
    };
    // All this just due to iframes with srcdoc bug
    utils.replaceWithProxy(document, "createElement", createElementHandler);
  };

  // Let's go
  addIframeCreationSniffer();
} catch (err) {
  // console.warn(err)
}