Framebus

Framebus allows you to easily send messages across frames (and iframes)
with a simple bus.

In one frame:

 var Framebus = require("framebus");
var bus = new Framebus();

bus.emit("message", {
  from: "Ron",
  contents: "they named it...San Diago",
});

In another frame:

 var Framebus = require("framebus");
var bus = new Framebus();

bus.on("message", function (data) {
  console.log(data.from + " said: " + data.contents);
});

The Framebus class takes a configuration object, where all the params
are optional.

 type FramebusOptions = {
  origin?: string, // default: "*"
  channel?: string, // no default
  verifyDomain?: (url: string) => boolean, // no default
  targetFrames?: <HTMLFrameElement | Window>[], // by default, all frames available to broadcast to
};

The origin sets the framebus instance to only operate on the chosen
origin.

The channel namespaces the events called with on and emit so you
can have multiple bus instances on the page and have them only
communicate with busses with the same channel value.

If a verifyDomain function is passed, then the on listener will only
fire if the domain of the origin of the post message matches the
location.href value of page or the function passed for verifyDomain
returns true.

 var bus = new Framebus({
  verifyDomain: function (url) {
    // only return true if the domain of the url matches exactly
    url.indexOf("https://my-domain") === 0;
  },
});

If a targetFrames array is passed, then framebus will only send
messages to those frames and listen for messages from those frames. You
can pass a reference to a Window (the return value of window.open)
or an HTMLFrameElement (a DOM node representing an iframe).

 var myIframe = document.getElementById("my-iframe");

var bus = new Framebus({
  targetFrames: [myIframe],
});

To add additional frames to the targetFrames array in the future, use
the addTargetFrame method. targetFrames must be set, even if it's an
empty array, for this method to work.

 var myIframe = document.getElementById("my-iframe");

var bus = new Framebus({
  targetFrames: [],
});

bus.addTargetFrame(myIframe);

API

target(options: FramebusOptions): framebus

returns: a chainable instance of framebus that operates on the
chosen origin.

This method is used in conjuction with emit, on, and off to
restrict their results to the given origin. By default, an origin of
'*' is used.

 framebus
  .target({
    origin: "https://example.com",
  })
  .on("my cool event", function () {});
// will ignore all incoming 'my cool event' NOT from 'https://example.com'

emit('event', data?, callback?): boolean

returns: true if the event was successfully published, false
otherwise

emitAsPromise('event', data?): Promise

returns: A promise that resolves when the emitted event is responded
to the first time. It will reject if the event could not be succesfully
published.

Using this method assumes the browser context you are using supports
Promises. If it does not, set a polyfill for the Framebus class with
setPromise

 // or however you want to polyfill the promise
const PolyfilledPromise = require("promise-polyfill");

Framebus.setPromise(PolyfilledPromise);

on('event', fn): boolean

returns: true if the subscriber was successfully added, false
otherwise

Unless already bound to a scope, the listener will be executed with
this set to the MessageEvent received over
postMessage.

off('event', fn): boolean

returns: true if the subscriber was successfully removed, false
otherwise

include(popup): boolean

returns: true if the popup was successfully included, false
otherwise

 var popup = window.open("https://example.com");

framebus.include(popup);
framebus.emit("hello popup and friends!");

addTargetFrame(frame): boolean

Used in conjunction with targetFrames configuration. If a
targetFrames array is not passed on instantiation, this method will
noop.

 var frame = document.getElementById("my-iframe");

framebus.addTargetFrame(frame);
framebus.emit("hello targetted iframe!");

teardown(): void

Calls off on all listeners used for this bus instance and makes
subsequent calls to all methods noop.

 bus.on("event-name", handler);

// event-name listener is torn down
bus.teardown();

// these now do nothing
bus.on("event-name", handler);
bus.emit("event-name", data);
bus.off("event-name", handler);

Pitfalls

These are some things to keep in mind while using framebus to handle
your event delegation

Cross-site scripting (XSS)

framebus allows convenient event delegation across iframe borders.
By default it will broadcast events to all iframes on the page,
regardless of origin. Use the optional target() method when you know
the exact domain of the iframes you are communicating with. This will
protect your event data from malicious domains.

Data is serialized as JSON

framebus operates over postMessage using JSON.parse and
JSON.stringify to facilitate message data passing. Keep in mind that
not all JavaScript objects serialize cleanly into and out of JSON, such
as undefined.

Asynchronicity

Even when the subscriber and publisher are within the same frame, events
go through postMessage. Keep in mind that postMessage is an
asynchronous protocol and that publication and subscription handling
occur on separate iterations of the event loop
(MDN).

Published callback functions are an abstraction

When you specify a callback while using emit, the function is not
actually given to the subscriber. The subscriber receives a one-time-use
function that is generated locally by the subscriber's framebus.
This one-time-use callback function is pre-configured to publish an
event back to the event origin's domain using a
UUID as the event name. The events
occur as follows:

1. http://emitter.example.com publishes an event with a function as
   the event data

    var callback = function (data) {
     console.log("Got back %s as a reply!", data);
   };
   
   framebus.emit("Marco!", callback, "http://listener.example.com");
   

2. The framebus on http://emitter.example.com generates a UUID as
   an event name and adds the callback as a subscriber to this event.

3. The framebus on http://listener.example.com sees that a
   special callback event is in the event payload. A one-time-use
   function is created locally and given to subscribers of 'Marco!'
   as the event data.

4. The subscriber on http://listener.example.com uses the local
   one-time-use callback function to send data back to the emitter's
   origin

    framebus
     .target("http://emitter.example.com")
     .on("Marco!", function (callback) {
       callback("Polo!");
     });
   

5. The one-time-use function on http://listener.example.com publishes
   an event as the UUID generated in step 2 to the origin that
   emitted the event.

6. Back on http://emitter.example.com, the callback is called and
   unsubscribed from the special UUID event afterward.

Development and contributing

See CONTRIBUTING.md