How to Build an Easy Embedabble Widget

by George Brassey


  • Developer at The Mechanism
  • Full Stack — JavaScript, PHP and a little ruby

Bug Tracker

Fly trap — Front end widget for collecting bugs

  • Simple interface for clients to comunicate issues
  • Provides additional information, such as:
    • Screen Size
    • Operating System
    • Browser information

What is a Widget?

  • An embedded service
  • Modular — Deploy once / use many times


  • Unobtrusive with dynamic interaction
    • Hide when not in use
    • Slide into place when called
  • Responsive
  • Outside the flow of the DOM
  • Sandboxed so that it doesn’t cause any conflicts with the project DOM, JS or CSS
  • Context Aware: the widget needs to receive infomation from the container
  • Deploy on a unique server and implement across many projects


  • Service: The bug collector in the iframe
  • Parent: Container or the project under tracking


  • Bug tracker sits inconspicuosly in the bottom left corner
  • Dynamic — widget slides into view when necessary
  • Responsive to fit on all device sizes

Iframes — The Good

  • Sandboxed - protects from conflict and spillover

Iframes — The Bad

  • Same-origin policy blocks communication between parent and child documents when service is loaded from another domain
    • Unable to receive necessary information from the child

HTML5 postMessage

  • Method to send messages between documents
  • New specification. Does not work on older browsers

Remote Procedure Call and easyXDM

  • Remote Procedure Call (RPC) — protocol for remote invocation
  • easyXDM — a library that leverages RPC for cross origin communication between documents
    • Methods can be made open to the other context
    • Eg. The child can initiate a method which will run in the parent and wait for return value

Embedding the Iframe

// Create iframe container
var iframeContainer = document.createElement('div');

// Create RPC instance
var rpc = new easyXDM.Rpc({
	remote: '',
	container: iframeContainer,
	props: {
		frameborder: '0',
		scrolling: 'no',
		allowTransparency: 'true',
		style: {
			height: '100%',
			width: '100%',
			display: 'block'
	local: {
		parentInfo: function () {
			return {
				width: window.innerWidth || document.documentElement.clientWidth || document.body.clientWidth,
				height: window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight,
				url: window.location.href

... And on the service side

var rpc = new easyXDM.Rpc({},
    remote: {
        parentInfo: {}

rpc.parentInfo(function(parentInfo) {
    // do something with...
    diagnosticInfo = {
        'width' = parentInfo.width,
        'height' = parentInfo.height,
        'url' = parentInfo.url


Why Cross Domain and Iframes?

Card UI

Card UI

What is Card UI?

Google Now

google now

Why is Card UI important?

  • Can be used to embed foreign services within your website, webapp, native app
  • No standard exists and current implementations are difficult
  • Context aware services will be better when they can communicate with their container

Further Reading

  • is an open source initiative to create a Card Ecosystem
    • Oasis.jsA lightweight library for embedding untrusted content and exposing capabilities
  • Google Polymer — a library built on Web Components for creating custom elements

The End

by George Brassey