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Urbini is a mobile web framework that helps web apps and native apps work together in one network.

Physics UI

In 2013 the design went flat. In 2014 the focus in mobile web apps is on realistic, fluid, intuitive motion. iOS and native apps serve to us as a shiny beacon here. To give web apps an edge, we integrated Urbini with a physics engine (and are working with another physics engine developer to offer you more choices).

We started with a very difficult control, an infinite scroll with momentum and edge bounces. It works for a full page vertically or horizontally, or as a strip, like still shots in IMDB app. Not only this control handles millions of rows on the tinyest of mobile devices, it provides the cool way to control its physics, the air drag, the spring stiffness and damping.

More controls with simulas for mass, gravity, friction, magnetic snaps will follow. We want devs to choose from a gallery of buttery smooth cool movements to drop into their apps. Read up, we'll talk about physics more a bit later.

Each app is a platform

What developer does not secretly hope to turn his app into a platform? With our IFTTT-inspired design your app will automatically serve as a hub to the complementary apps. For those familiar with IFTTT, here is a compare-and-contrast checklist:

  1. Like IFTTT, Urbini aspires to connect apps and devices (Internet of Things)

  2. Unlike IFTTT, Urbini is for mobile web, facilitating app and device connections on smartphones and tablets.

  3. Unlike IFTTT it is open, all connectivity code is here on github. And unlike IFTTT, channels (maps to existing apps) can be created by anyone.

  4. Unlike IFTTT it is more programmable. All app inter-connections are unified via [backbone] data models, and for each connection you can add a small JavaScript.

The Appnet

Think of app networking in Urbini, as mashups++. Instead of the custom ad-hoc code connecting the apps, the Appnet offers a unified method of mapping any webapi into a browser-based database. Apps can now use data from multiple sites as if it was one site (see an article on Appnet and its goals).

Here are the steps:

  1. Use mobile/tablet browser create an App on In desktop browser go to To start app creation click on App gallery and click on + icon in navbar.

  2. Using a browser define backbone model(s) that will be created from a WebAPI.

  3. Each model has a property sync. Paste into it an adapter script that will map json returned by site's WebAPI into backbone model objects. See Urbien Groupon app as a sample. To preserve quality and lower the noise, the new App initially shows up in App Ideas. When 3 people install it, it will show up in App Gallery.

  4. Not just the site's owner, but anyone can create an app, models and adapter for someone else's site. And anyone can create IFTTT-like connectors between the apps using simple JavaScript.

App dev for the rest of us

Urbini lifts mobile web apps to the level of native apps and then helps them work together in one network, thus making the mobile app dev field more open. @urbien we set out to build tools for ourselves to produce mobile web apps much faster. Then we realized that others could use the same tools. Thus Urbini was conceived. But we wanted to take Urbini much further. Our vision is to open mobile app dev to non-professional developers. Here is the architecture that we created to make this happen.

Data binding ++

MVC framewokslike Backbone have drastically changed the way we build Web apps, moving most of app dev from the server to the browser side.

Require.js and other AMD loaders emerged to address the greater weight and complexity of such web apps. UI frameworks, like Bootstrap, Topcoat, Building Blocks, jQuery Mobile have offered great skins, and the JS libraries, like the masonry (isotope, infinity, packery, etc.), mobiscroll, leaflet, d3, etc. are making writing apps entirely on the client side possible.

Now Push notifications have arrived for web apps. With push notifications Chrome, Firefox and Safari are establishing the parity with the native apps for background operations. And pushing forward, HTML5 WebRTC gives web apps Skype-like functionality, something that only a handful of native apps can do.

HTML5 on mobile is 10x more complex

While all this web tech helps, the complexity of putting all the pieces together has gone up 10x times. Yet the major problem of reaching native performance has still not been solved. To get there Urbini offers several components.

First one is bootstrapping all app assets, storing them on mobile and incrementally updating them without bothering the user. This achieves the offline support basis and speeds up app startup.

Then, to be fast like native apps we must paint from the local data store (in the current HTML5 world that means using a hodge podge of offline storage methods, each with its own limitations: IndexedDB/WebSQL/LocalStorage/Appcache/FileSystem). Then we need to sync the data between the web site and local storage, seamlessly behind the scenes. Then we need to upgrade local db schema gradually and in the way that user does not notice it. And we must at all cost keep away from the main UI thread, since Javascript UI is singlethreaded.

Urbini is solving all these problems. We think of Urbini as a first distro for Javascript. A boot loader, a packager, build tools, web db sync, an a UI package for apps. We want as much of it as possible to be replaceble with open source components that you prefer, e.g. a Pure CSS framework of your choice.

Mobile HTML5 performance gap

Painting UI from the local database and making app assets available offline is the core of Urbini, but this is not enough to make mobile HTML5 buttery smooth. To close the gap with the native apps we had to employ the bag of tricks developed by LinkedIn, [Sencha] ( and [] (

  1. Lazy load images. This is a standard technique for image heavy sites even of the desktop. We augmented it with the offline image support. We are saving all images into IndexedDB so that we do not need to request them from the server again and so that users could see images offline. (IndexedDB in Firefox, an IndexedDB shim on top of WebSQL in Safari, and using a File System in Chrome, as it's IndexedDB does not support Blobs yet).

  2. DOM on a strict diet. As the number of DOM elements grows DOM manipulation becomes extremely slow. LinkedIn team graciously shared their layered sliding window method. Sencha and also use sliding window, but do not provide much details (In all fairness one could read their code, but is not small). Our sliding window algorithm adapts to the direction (vertical or horizontal), the capabilities of the device (low end or older phones and tablets with 256M ram) and the speed of user's actions.

  3. Show results ASAP. When Sencha developers analyzed the Facebook HTML5 app, which Facebook abandoned for for performance reasons, they were shocked to see that every WebAPI request was bringing 20K+ data, see Bonus Points paragraph in Fastbook article. Thus Urbini requests data for resource lists from Urbien cloud database in two steps: a small subset of properties is requested initially and the rest is requested later. In a similar fashion, when painting user's profile we show a part of the page right away and then paint the rest of it later, e.g. user's friend list, a call-in-progress header, etc. (When Urbini app is based on third-party WebAPIs, this optimization technique is not used).

  4. App Homepage. This is a continuation of a previous theme. App's Homepage has to load fast, letting the rest of the framework and app assets load later. Homepage is stripped of all Urbini dependencies, and uses dataurl images so that it loads faster and can work offline.

  5. Avoid long runs. It is critical to not keep main JS thread busy with long tasks. As one measure, we use a pool of JS threads to do some processing off-main-thread. For example, Urbini executes all xhr requests on web workers. This a simple and commonly used technique. Sencha introduced a greatly more complex technique - to chunk up all the work into small tasks and queue them up for execution at the appropriate time (queue is driven by rAF, introduced below).

  6. Smooth animations. rAF feature in modern browsers is a key to the most sophisticated performance solutions, so it pays to grok it. Browser calls our rAF callback to let us paint a frame. rAF callback is called with the frequency of a refresh rate of your monitor (usually 60hz) , so if we manage to fit into the time slot allotted to us by rAF, then DOM manipulation, transitions, etc. will look smoother to the user. So debouncing is a simple technique where you only make a record of what needs to be done in various event handlers that process user actions, such as touchstart, mouseover, click, etc. and DO NOT manipulate DOM there, only manipulate it in the rAF callback. In that sense rAF is like a conveyor belt, you have limited time to do your small operation and you can not delay, as you will stop the whole belt.

  7. Responsive images. The problem is that mobile devices have a whole slew of sizes and resolutions. The other problem is user's network can be fast and unlimited or slow and metered. Thus we can not serve the same high DPI image to iPad with retina screen and to FirefoxOS ZTE Open. Images are pregenerated at a multitude of sizes on Urbien server and are served according to the device's screen size and resolution. Expensive image scaling on the device is avoided, when appropriate.

  8. DOM optimizations. DOM elements reuse, Read/write ops batching, off-DOM painting using documentFragment, innerHtml batching (concatenate a string and insert the result with one innerHtml), reflow avoidance, and many other tricks are employed by Urbini.

  9. Pre-fetching. Data for the next page user is likely to want is pre-fetched and sometimes even pre-rendered. This applies to the menu items, next page for the infinite scrolling, etc. The key is to queue these tasks with the lower priority so that they execute when user is idle and browser is idle and drop these tasks from the queue if user moved to a different screen.

  10. Instant reaction to user actions. We aim to start transitions right after user actions. This work is in progress. We also process touch events ourselves to avoid unnecessary painting on scroll swipes (like hover highlighting) and to determine user gestures, like taps, vertical and horizontal flicks and a lot more gestures in the future.

More optimizations are planned:

  1. Bundling/batching WebAPI requests. Sometimes we issue a set of WebAPI requests in the row. Most our WebAPI requests can be delayed, as pages are painted from the local DB, so we could debounce async requests and issue one batch request to the Urbien cloud server. If app has its backend on a third-party cloud server, we would continue to issue WebAPI requests one by one.

  2. Simple Physics. iOS's delightful momentum scrolling, scroll end bounce are examples of mimicking real-life forces to give user's subconscious the cues on [what is going on and what to expect next] ( But may be the biggest advantage of using the Physics engine is its power of illusion. Apparently [when screen movements match what our brains got wired to perceive in the real world] ( the jittery movements will look silky smooth to the user. CSS transform provides built-in animation easing, but it is arrow prone to derailing by sudden wind blows. As JS's sudden Garbage Collection, background apps and user actions often throw us those unexpected blows, the Physics engine helps us make recalculate our next move in-flight and on every frame. We use matrix3D CSS transforms for that.


Help us edit a wiki to teach newbies how to build mobile web apps really fast. These apps start with just a model that is created in the web browser, even on a smartphone. They offer 100% generated UI which can later be customized, provide full offline support, feature built in social login (to 5+ networks) and automatic social reposting, have profile import and friend invite, e-commerce capabilities, image galleries and a lot more, without newly christened developer lifting a finger. For professional developers these apps are a great starting point to modify our templates, views, and to start experimenting with app networking, without being bogged down with the usual build up of the core app functionality.

Please join us in this amazing journey of making the Web open again.

Gene, Ellen, Jacob, Mark, Simon, Alex and the rest of Urbien team. Visit Urbien to learn more about us.

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