fune/browser/components/pocket/content/panels/js/messages.js

// Documentation of methods used here are at:
// https://developer.mozilla.org/en-US/Add-ons/Code_snippets/Interaction_between_privileged_and_non-privileged_pages

var pktPanelMessaging = (function() {
  function panelIdFromURL(url) {
    var panelId = url.match(/panelId=([\w|\d|\.]*)&?/);
    if (panelId && panelId.length > 1) {
      return panelId[1];
    }

    return 0;
  }

  function prefixedMessageId(messageId) {
    return "PKT_" + messageId;
  }

  function panelPrefixedMessageId(panelId, messageId) {
    return prefixedMessageId(panelId + "_" + messageId);
  }

  function addMessageListener(panelId, messageId, callback) {
    document.addEventListener(
      panelPrefixedMessageId(panelId, messageId),
      function(e) {
        callback(JSON.parse(e.target.getAttribute("payload"))[0]);

        // TODO: Figure out why e.target.parentNode is null
        // e.target.parentNode.removeChild(e.target);
      }
    );
  }

  function removeMessageListener(panelId, messageId, callback) {
    document.removeEventListener(
      panelPrefixedMessageId(panelId, messageId),
      callback
    );
  }

  function sendMessage(panelId, messageId, payload, callback) {
    // Payload needs to be an object in format:
    // { panelId: panelId, data: {} }
    var messagePayload = {
      panelId,
      data: payload || {},
    };

    // Create a callback to listen for a response
    if (callback) {
      var messageResponseId = messageId + "Response";
      var responseListener = function(responsePayload) {
        callback(responsePayload);
        removeMessageListener(panelId, messageResponseId, responseListener);
      };

      addMessageListener(panelId, messageResponseId, responseListener);
    }

    // Send message
    var element = document.createElement("PKTMessageFromPanelElement");
    element.setAttribute("payload", JSON.stringify([messagePayload]));
    document.documentElement.appendChild(element);

    var evt = document.createEvent("Events");
    evt.initEvent(prefixedMessageId(messageId), true, false);
    element.dispatchEvent(evt);
  }

  /**
   * Public functions
   */
  return {
    panelIdFromURL,
    addMessageListener,
    removeMessageListener,
    sendMessage,
  };
})();