Sencha Touch 2 – Thoughts from the Trenches

As you may have seen, we put out the first public preview release of Sencha Touch 2 today. It only went live a few hours ago but the feedback has been inspiring so far. For the full scoop see the post on the sencha.com blog. A few thoughts on where we are with the product:

Performance

Performance on Android devices in particular is breathtaking. I never thought I’d see the day where I could pick up an Android 2.3 device and have it feel faster than an iPhone 4, and yet that’s exactly what Sencha Touch 2 brings to the table. I recorded this short video on an actual device to show real world performance:

Now try the same on Sencha Touch 1.x (or any other competing framework) and (if you’re anything like me) cringe at what we were accustomed to using before. That video’s cool, but the one that’s really driving people wild is the side by side comparison of the layout engines in 1.x and 2.x.

Getting our hands on a high speed camera and recording these devices at 120fps was a lot of fun. Slowing time down to 1/4 of normal speed shows just how much faster the new layout engine is than what we used to have:

The most amazing part here is that we actually finish laying out *before* the phone’s rotation animation has completed. Skipping through the video frame by frame there are at least 5 frames where the app is fully laid out and interactive while the phone’s rotation animation is still running. Beating the phone’s own rotation speed is the holy grail – it’s not possible to make it any faster.

Documentation

I’ll admit it, I’m fanatical about great documentation. I’m sure I drive everyone else on the team crazy but I think it’s worth it. This is only a preview release but it already contains by far the best, most complete documentation we’ve ever shipped in an initial release.

In fact, the team’s worked so hard on documenting classes that it’s probably better than the (already good) Ext JS 4 docs. Naturally, this makes it time to further improve the Ext JS documentation.

We’ve added some awesome features here – lots of videos, 11 brand new guides and illustrations. My favourite new feature is definitely the inline examples with live previews though – seeing Sencha Touch running live in a phone/tablet right there in the docs is just amazing. Little gems like the live twitter feed in the bottom-most example in the DataView docs really sell just how easy it is to configure these components.

We set a high bar for this though. We’ve gone from woeful documentation in 1.x to good documentation in 2.x, but what we’re shooting for is excellence. We’ll continue to round out our content over coming weeks, and have a few new features rolling out soon that will raise the bar once again.

Onwards

We have a few features left to implement, which is why we’re calling this preview and not beta. Probably the biggest thing now is getting routing/deep linking back into the framework, along with a nice new syntax that I think you’ll find really easy to use. We’re also missing carousel animations and a handful of other things that will be going back in over the coming weeks. We have Sencha Con 2011 in just 12 days now though so we’ll share more details there.

Finally though, I want to thank everyone who participated in the closed preview phase, and for everyone sending their support and kind words on the blog, the forums and on twitter. We really appreciate all the great feedback and I hope we can exceed your expectations with a fast, polished, gorgeous 2.0 final!

SourceDevCon 2011 – an awesome conference

The inaugural SouceDevCon just wrapped up in Split, Croatia so I’d like to share a few thoughts on the last few days. The conference was an enormous success, featuring some great speakers, inspiring presentations and a fantastic group of attendees. Split itself is beautiful, and the weather was equally equitable. More than a few of us are returning a lot browner/redder than we came.

Grgur

Day 1

The conference was spread across 3 days – the first two were spent listening and learning across the three concurrent tracks, the third on a boat sailing around the Adriatic Sea. Day one kicked off with my colleagues Aditya and James setting out a little of what to expect from Sencha in 2011 in the opening keynote.

Straight after that I took to the stage to introduce a few of the features of Ext JS 4. My session started a little late and I forgot what I was talking about a couple of times (sorry guys 🙂 ) but I think it turned out well enough. I spliced together the deadly combination of sleep deprivation and live coding but with a little help from the audience we were able to stumble through. I think it would make for a good screencast.

Aditya came on next and introduced our new Sencha.IO services, which seem to have garnered a lot of interest. James showed off the new Ext JS 4 theming support using SASS and Compass and Nils Dehl did a great job explaining the Ext.data and Ext.direct packages. Jay Garcia gave a well-received talk on creating extensions and plugins, during which I think a lot of people learned a great deal about how classes work in Ext JS 4. I also very much enjoyed Tomislav Car’s investigation into getting Sencha Touch to run on phones other than Androids and iPhones.

Day 1 ended with a long party (I counted at least 8 hours) with inordinate amounts of Croatian beer, which went down very well. It was great meeting so many new people and hearing how much people are getting out of Ext JS and Sencha Touch, as well as what we can improve.

Day 2

Day 2 started in a somewhat hungover fashion with some awesome material from our very own Brian Moeskau, who demonstrated how to use the 3.x -> 4.x compatibility file, upgrading an application from 3.3.1 to 4.0.0 in front of our eyes. Nige (Animal) White demonstrated several of Ext JS’s layout managers before giving one of the highlights of the conference in his debugging JavaScript presentation (by contrast he calls the introduction of errors into code “bebugging”).

Tobias Uhlig showed off FieldManager, a sports centre management management application with a Sencha Touch mobile app, while Matz Bryntse and Brian Moeskau demoed their awesome Scheduler and Calendar components. Josef Sakalos (Saki) spent the afternoon teaching people to use Ext JS 4’s new MVC package, which makes writing apps a faster and more enjoyable experience. He is an excellent teacher.

Our host the inimitable Grgur finished things off with a typically heartfelt ending keynote to wrap up the business end of the conference. The evening was a great opportunity to see some of Split and spend an enjoyable meal with Croatian locals Tomislav, Miro and the ever-logical Lucia. Unfortunately their attempts to teach me Croatian did not yield much success.

Day 3

Day 3 was a stroke of genius by Grgur. We took a chartered boat down to the town and looked around the old Roman-era palace. The boat was well stocked with beer and with so many community members in one place the conversation was pretty lively. All of this relaxing was great but with a head full of ideas I’m anxious to get back to California and better tune our products based on all the feedback I received this week.

All of the sessions were recorded on video and I believe they’ll be made available in around a month’s time. If you can’t wait until then we have a meetup schedule for May 23rd hosted at Sencha HQ in northern California, to which you’re all invited. Just in case you’ve never been to Split before perhaps the sight that greeted us when we arrived will prompt you to get yourself on a flight.

adriatic

Proxies in Ext JS 4

One of the classes that has a lot more prominence in Ext JS 4 is the data Proxy. Proxies are responsible for all of the loading and saving of data in an Ext JS 4 or Sencha Touch application. Whenever you’re creating, updating, deleting or loading any type of data in your app, you’re almost certainly doing it via an Ext.data.Proxy.

If you’ve seen January’s Sencha newsletter you may have read an article called Anatomy of a Model, which introduces the most commonly-used Proxies. All a Proxy really needs is four functions – create, read, update and destroy. For an AjaxProxy, each of these will result in an Ajax request being made. For a LocalStorageProxy, the functions will create, read, update or delete records from HTML5 localStorage.

Because Proxies all implement the same interface they’re completely interchangeable, so you can swap out your data source – at design time or run time – without changing any other code. Although the local Proxies like LocalStorageProxy and MemoryProxy are self-contained, the remote Proxies like AjaxProxy and ScriptTagProxy make use of Readers and Writers to encode and decode their data when communicating with the server.

Proxy-Reader-and-Writer

Whether we are reading data from a server or preparing data to be sent back, usually we format it as either JSON or XML. Both of our frameworks come with JSON and XML Readers and Writers which handle all of this for you with a very simple API.

Using a Proxy with a Model

Proxies are usually used along with either a Model or a Store. The simplest setup is just with a model:

var User = Ext.regModel('User', {
    fields: ['id', 'name', 'email'],
    
    proxy: {
        type: 'rest',
        url : '/users',
        reader: {
            type: 'json',
            root: 'users'
        }
    }
});

Here we’ve created a User model with a RestProxy. RestProxy is a special form of AjaxProxy that can automatically figure out Restful urls for our models. The Proxy that we set up features a JsonReader to decode any server responses – check out the recent data package post on the Sencha blog to see Readers in action.

When we use the following functions on the new User model, the Proxy is called behind the scenes:

var user = new User({name: 'Ed Spencer'});

//CREATE: calls the RestProxy's create function because the user has never been saved
user.save();

//UPDATE: calls the RestProxy's update function because it has been saved before
user.set('email', 'ed@sencha.com');

//DESTROY: calls the RestProxy's destroy function
user.destroy();

//READ: calls the RestProxy's read function
User.load(123, {
    success: function(user) {
        console.log(user);
    }
});

We were able to perform all four CRUD operations just by specifying a Proxy for our Model. Notice that the first 3 calls are instance methods whereas the fourth (User.load) is static on the User model. Note also that you can create a Model without a Proxy, you just won’t be able to persist it.

Usage with Stores

In Ext JS 3.x, most of the data manipulation was done via Stores. A chief purpose of a Store is to be a local subset of some data plus delta. For example, you might have 1000 products in your database and have 25 of them loaded into a Store on the client side (the local subset). While operating on that subset, your user may have added, updated or deleted some of the Products. Until these changes are synchronized with the server they are known as a delta.

In order to read data from and sync to the server, Stores also need to be able to call those CRUD operations. We can give a Store a Proxy in the same way:

var store = new Ext.data.Store({
    model: 'User',
    proxy: {
        type: 'rest',
        url : '/users',
        reader: {
            type: 'json',
            root: 'users'
        }
    }
});

We created the exact same Proxy for the Store because that’s how our server side is set up to deliver data. Because we’ll usually want to use the same Proxy mechanism for all User manipulations, it’s usually best to just define the Proxy once on the Model and then simply tell the Store which Model to use. This automatically picks up the User model’s Proxy:

//no need to define proxy - this will reuse the User's Proxy
var store = new Ext.data.Store({
    model: 'User'
});

Store invokes the CRUD operations via its load and sync functions. Calling load uses the Proxy’s read operation, which sync utilizes one or more of create, update and destroy depending on the current Store delta.

//CREATE: calls the RestProxy's create function to create the Tommy record on the server
store.add({name: 'Tommy Maintz'});
store.sync();

//UPDATE: calls the RestProxy's update function to update the Tommy record on the server
store.getAt(1).set('email', 'tommy@sencha.com');
store.sync();

//DESTROY: calls the RestProxy's destroy function
store.remove(store.getAt(1));
store.sync();

//READ: calls the RestProxy's read function
store.load();

Store has used the exact same CRUD operations on the shared Proxy. In all of the examples above we have used the exact same RestProxy instance from three different places: statically on our Model (User.load), as a Model instance method (user.save, user.destroy) and via a Store instance (store.load, store.sync):

Proxy-reuse

Of course, most Proxies have their own private methods to do the actual work, but all a Proxy needs to do is implement those four functions to be usable with Ext JS 4 and Sencha Touch. This means it’s easy to create new Proxies, as James Pearce did in a recent Sencha Touch example where he needed to read address book data from a mobile phone. Everything he does to set up his Proxy in the article (about 1/3rd of the way down) works the same way for Ext JS 4 too.

Introduction to Ext JS 4

At the end of last 2010 we capped off an incredible year with SenchaCon – by far the biggest gathering of Sencha developers ever assembled. We descended on San Francisco, 500 strong, and spent an amazing few days sharing the awesome new stuff we’re working on, learning from each other, and addressing the web’s most pressing problems.

Now, we’re proud to release all of the videos from the conference completely free for everyone. You can see a full list on our conference site, where you’ll find days worth of material all about Ext JS 4, Sencha Touch and all of the other treats we’re working on at the moment.

Some of the videos in particular stand out for me – Jamie’s Charting and Layouts talks were spectacular, as was Rob’s Theming Ext JS 4 talk. On the Touch side, Tommy’s talks on Performance and Debugging are required viewing, as is Dave Kaneda’s characteristically off the cuff Theming talk.

My personal high point was standing in front of all of you and introducing Ext JS 4 and its three core goals – speed, stability and ease of use. I think you’re going to love what we’ve done with the framework in version 4, but for now I’ll let the video do the talking:

If you’re so inclined, you can find the slides for this talk on slideshare, and if you can still stand the sound of my voice check out my other presentation on Ext JS 4 Architecture, focusing chiefly on the new data package (slides).

Ext JS 4: The Class Definition Pipeline

Last time, we looked at some of the features of the new class system in Ext JS 4, and explored some of the code that makes it work. Today we’re going to dig a little deeper and look at the class definition pipeline – the framework responsible for creating every class in Ext JS 4.

As I mentioned last time, every class in Ext JS 4 is an instance of Ext.Class. When an Ext.Class is constructed, it hands itself off to a pipeline populated by small, focused processors, each of which handles one part of the class definition process. We ship a number of these processors out of the box – there are processors for handling mixins, setting up configuration functions and handling class extension.

The pipeline is probably best explained with a picture. Think of your class starting its definition journey at the bottom left, working its way up the preprocessors on the left hand side and then down the postprocessors on the right, until finally it reaches the end, where it signals its readiness to a callback function:

Processors

The distinction between preprocessors and postprocessors is that a class is considered ‘ready’ (e.g. can be instantiated) after the preprocessors have all been executed. Postprocessors typically perform functions like aliasing the class name to an xtype or back to a legacy class name – things that don’t affect the class’ behavior.

Each processor runs asynchronously, calling back to the Ext.Class constructor when it is ready – this is what enables us to extend classes that don’t exist on the page yet. The first preprocessor is the Loader, which checks to see if all of the new Class’ dependencies are available. If they are not, the Loader can dynamically load those dependencies before calling back to Ext.Class and allowing the next preprocessor to run. We’ll take another look at the Loader in another post.

After running the Loader, the new Class is set up to inherit from the declared superclass by the Extend preprocessor. The Mixins preprocessor takes care of copying all of the functions from each of our mixins, and the Config preprocessor handles the creation of the 4 config functions we saw last time (e.g. getTitle, setTitle, resetTitle, applyTitle – check out yesterday’s post to see how the Configs processor helps out).

Finally, the Statics preprocessor looks for any static functions that we set up on our new class and makes them available statically on the class. The processors that are run are completely customizable, and it’s easy to add custom processors at any point. Let’s take a look at that Statics preprocessor as an example:

//Each processor is passed three arguments - the class under construction,
//the configuration for that class and a callback function to call when the processor has finished
Ext.Class.registerPreprocessor('statics', function(cls, data, callback) {
    if (Ext.isObject(data.statics)) {
        var statics = data.statics,
            name;
        
        //here we just copy each static function onto the new Class
        for (name in statics) {
            if (statics.hasOwnProperty(name)) {
                cls[name] = statics[name];
            }
        }
    }

    delete data.statics;

    //Once the processor's work is done, we just call the callback function to kick off the next processor
    if (callback) {
        callback.call(this, cls, data);
    }
});

//Changing the order that the preprocessors are called in is easy too - this is the default
Ext.Class.setDefaultPreprocessors(['extend', 'mixins', 'config', 'statics']);

What happens above is pretty straightforward. We’re registering a preprocessor called ‘statics’ with Ext.Class. The function we provide is called whenever the ‘statics’ preprocessor is invoked, and is passed the new Ext.Class instance, the configuration for that class, and a callback to call when the preprocessor has finished its work.

The actual work that this preprocessor does is trivial – it just looks to see if we declared a ‘statics’ property in our class configuration and if so copies it onto the new class. For example, let’s say we want to create a static getNextId function on a class:

Ext.define('MyClass', {
    statics: {
        idSeed: 1000,
        getNextId: function() {
            return this.idSeed++;
        }
    }
});

Because of the Statics preprocessor, we can now call the function statically on the Class (e.g. without creating an instance of MyClass):

MyClass.getNextId(); //1000
MyClass.getNextId(); //1001
MyClass.getNextId(); //1002
... etc

Finally, let’s come back to that callback at the bottom of the picture above. If we supply one, a callback function is run after all of the processors have run. At this point the new class is completely ready for use in your application. Here we create an instance of MyClass using the callback function, guaranteeing that the dependency on Ext.Window has been honored:

Ext.define('MyClass', {
    extend: 'Ext.Window'
}, function() {
   //this callback is called when MyClass is ready for use
   var cls = new MyClass();
   cls.setTitle('Everything is ready');
   cls.show();
});

That’s it for today. Next time we’ll look at some of the new features in the part of Ext JS 4 that is closest to my heart – the data package.

Classes in Ext JS 4: Under the hood

Last week we unveiled a the brand new class system coming in Ext JS 4. If you haven’t seen the new system in action I hope you’ll take a look at the blog post on sencha.com and check out the live demo. Today we’re going to dig a little deeper into the class system to see how it actually works.

To briefly recap, the new class system enables us to define classes like this:

Ext.define('Ext.Window', {
    extend: 'Ext.Panel',
    requires: 'Ext.Tool',
    mixins: {
        draggable: 'Ext.util.Draggable'
    },
    
    config: {
        title: "Window Title"
    }
});

Here we’ve set up a slightly simplified version of the Ext.Window class. We’ve set Window up to be a subclass of Panel, declared that it requires the Ext.Tool class and that it mixes in functionality from the Ext.util.Draggable class.

There are a few new things here so we’ll attack them one at a time. The ‘extend’ declaration does what you’d expect – we’re just saying that Window should be a subclass of Panel. The ‘requires’ declaration means that the named classes (just Ext.Tool in this case) have to be present before the Window class can be considered ‘ready’ for use (more on class readiness in a moment).

The ‘mixins’ declaration is a brand new concept when it comes to Ext JS. A mixin is just a set of functions (and sometimes properties) that are merged into a class. For example, the Ext.util.Draggable mixin we defined above might contain a function called ‘startDragging’ – this gets copied into Ext.Window to enable us to use the function in a window instance:

//a simplified Draggable mixin
Ext.define('Ext.util.Draggable', {
    startDragging: function() {
        console.log('started dragging');
    }
});

When we create a new Ext.Window instance now, we can call the function that was mixed in from Ext.util.Draggable:

var win = Ext.create('Ext.Window');
win.startDragging(); //"started dragging"

Mixins are really useful when a class needs to inherit multiple traits but can’t do so easily using a traditional single inheritance mechanism. For example, Ext.Windows is a draggable component, as are Sliders, Grid headers, and many other UI elements. Because this behavior crops up in many different places it’s not feasible to work the draggable behavior into a single superclass because not all of those UI elements actually share a common superclass. Creating a Draggable mixin solves this problem – now anything can be made draggable with a couple of lines of code.

The last new piece of functionality I’ll mention briefly is the ‘config’ declaration. Most of the classes in Ext JS take configuration parameters, many of which can be changed at runtime. In the Ext.Window above example we declared that the class has a ‘title’ configuration, which takes the default value of ‘Window Title’. By setting the class up like this we get 4 methods for free – getTitle, setTitle, resetTitle and applyTitle.

  • getTitle – returns the current title
  • setTitle – sets the title to a new value
  • resetTitle – reverts the title to its default value (‘Window Title’)
  • applyTitle – this is a template method that you can choose to define. It is called whenever setTitle is called.

The applyTitle function is the place to put any logic that needs to be called when the title is changed – for example we might want to update a DOM Element with the new title:

Ext.define(‘Ext.Window’, {
    //..as above,
    
    config: {
        title: 'Window Title'
    },
    
    //updates the DOM element that contains the window title
    applyTitle: function(newTitle) {
        this.titleEl.update(newTitle);
    }
});

This saves us a lot of time and code while providing a consistent API for all configuration options: win-win.

Digging Deeper

Ext JS 4 introduces 4 new classes to make all this magic work:

  • Ext.Base – all classes inherit from Ext.Base. It provides basic low-level functionality used by all classes
  • Ext.Class – a factory for making new classes
  • Ext.ClassLoader – responsible for ensuring that classes are available, loading them if they aren’t on the page already
  • Ext.ClassManager – kicks off class creation and manages dependencies

These all work together behind the scenes and most of the time you won’t even need to be aware of what is being called when you define and use a class. The two functions that you’ll use most often – Ext.define and Ext.create – both call Ext.ClassManager under the hood, which in turn utilizes the other three classes to put everything together.

The distinction between Ext.Class and Ext.Base is important. Ext.Base is the top-level superclass for every class ever defined – every class inherits from Ext.Base at some point. Ext.Class represents the class itself – every class you define is an instance of Ext.Class, and a subclass of Ext.Base. To illustrate, let’s say we created a class called MyClass, which doesn’t extend any other class:

Ext.define('MyClass', {
    someFunction: function() {
        console.log('Ran some function');
    }
});

The direct superclass for MyClass is Ext.Base because we didn’t specify that MyClass should extend anything else. If you imagine a tree of all the classes we’ve defined so far, it will look something like this:

Sample-inheritance-tree

This tree bases its hierarchy on the inheritance structure of our classes, and the root is always Ext.Base – that is, every class eventually inherits from Ext.Base. So every item in the diagram above is a subclass of Ext.Base, but every item is also an instance of Ext.Class. Classes themselves are instances of Ext.Class, which means we can easily modify the Class at a later time – for example mixing in additional functionality:

//we can define some mixins at definition time
Ext.define('MyClass', {
    mixins: {
        observable: 'Ext.util.Observable'
    }
});

//it’s easy to add more later too
MyClass.mixin('draggable', 'Ext.util.Draggable');

This architecture opens up new possibilities for dynamic class creation and metaprogramming, which were difficult to pull off in earlier versions.

In the next episode, we’ll look at how the class definition pipeline is structured and how to extend it to add your own features.

Sencha Touch tech talk at Pivotal Labs

I recently gave an introduction to Sencha Touch talk up at Pivotal Labs in San Francisco. The guys at Pivotal were kind enough to record this short talk and share it with the world – it’s under 30 minutes and serves as a nice, short introduction to Sencha Touch:

Ed Spencer Sencha Touch tech talk

The slides are available on slideshare and include the code snippets I presented. The Dribbble example used in the talk is very similar to the Kiva example that ships with the Sencha Touch SDK, so I recommend checking that out if you want to dive in further.

Using the Ext JS PivotGrid

One of the new components we just unveiled for the Ext JS 3.3 beta is PivotGrid. PivotGrid is a powerful new component that reduces and aggregates large datasets into a more understandable form.

A classic example of PivotGrid’s usefulness is in analyzing sales data. Companies often keep a database containing all the sales they have made and want to glean some insight into how well they are performing. PivotGrid gives the ability to rapidly summarize this large and unwieldy dataset – for example showing sales count broken down by city and salesperson.

A simple example

We created an example of this scenario in the 3.3 beta release. Here we have a fictional dataset containing 300 rows of sales data (see the raw data). We asked PivotGrid to break the data down by Salesperson and Product, showing us how they performed over time. Each cell contains the sum of sales made by the given salesperson/product combination in the given city and year.

Let’s see how we create this PivotGrid:

var SaleRecord = Ext.data.Record.create([
    {name: 'person',   type: 'string'},
    {name: 'product',  type: 'string'},
    {name: 'city',     type: 'string'},
    {name: 'state',    type: 'string'},
    {name: 'month',    type: 'int'},
    {name: 'quarter',  type: 'int'},
    {name: 'year',     type: 'int'},
    {name: 'quantity', type: 'int'},
    {name: 'value',    type: 'int'}
]);

var myStore = new Ext.data.Store({
    url: 'salesdata.json',
    autoLoad: true,
    reader: new Ext.data.JsonReader({
        root: 'rows',
        idProperty: 'id'
    }, SaleRecord)
});

var pivotGrid = new Ext.grid.PivotGrid({
    title     : 'Sales Performance',
    store     : myStore,
    aggregator: 'sum',
    measure   : 'value',
    
    leftAxis: [
        {dataIndex: 'person',  width: 80},
        {dataIndex: 'product', width: 90}
    ],
    
    topAxis: [
        {dataIndex: 'year'},
        {dataIndex: 'city'}
    ]
});

The first half of this ought to be very familiar – we just set up a normal Record and Store. This is all we need to load our sample data so that it’s ready for pivoting. This is all exactly the same code as for our other Store-bound components like Grid and DataView so it’s easy to take an existing Grid and turn it into a PivotGrid.

The second half of the code creates the PivotGrid itself. There are 5 main components to a PivotGrid – the store, the measure, the aggregator, the left axis and the top axis. Taking these in turn:

  • Store – the Store we created above
  • Measure – the field in the data that we want to aggregate (in this case the sale value)
  • Aggregator – the function we use to combine data into the cells. See the docs for full details
  • Left Axis – the fields to break data down by on the left axis
  • Top Axis – the fields to break data down by on the top axis

The measure and the items in the axes must all be fields from the Store. The aggregator function can usually be passed in as a string – there are 5 aggregator functions built in: sum, count, min, max and avg.

Renderers

This is all we need to create a simple PivotGrid; now it’s time to look at a few more advanced options. Let’s start with renderers. Once the data for each cell has been calculated, the value is passed to an optional renderer function, which takes each value in turn and returns another value. One of the PivotGrid examples shows average heights in feet and inches but the calculated data is in decimal. Here’s the renderer we use in that example:

new Ext.grid.PivotGrid({
    store     : myStore,
    aggregator: 'avg',
    measure   : 'height',
    
    //turns a decimal number of feet into feet and inches
    renderer  : function(value) {
        var feet   = Math.floor(value),
            inches = Math.round((value - feet) * 12);
            
        return String.format("{0}' {1}"", feet, inches);
    },
    //the rest of the config
});

Customising cell appearance

Another one of the PivotGrid examples uses a custom cell style. As with the renderer, each cell has the opportunity to alter itself with a custom function – here’s the one we use in the countries example:

new Ext.grid.PivotGrid({
    store     : myStore,
    aggregator: 'avg',
    measure   : 'height',
    
    viewConfig: {
        getCellCls: function(value) {
            if (value < 20) {
                return 'expense-low';
            } else if (value < 75) {
                return 'expense-medium';
            } else {
                return 'expense-high';
            }
        }
    },
    //the rest of the config
});

Reconfiguring at runtime

A lot of the power of PivotGrid is that it can be used by users of your application to summarize datasets any way they want. This is made possible by PivotGrid’s ability to reconfigure itself at runtime. We present one final example of a PivotGrid that can be reconfigured at runtime. Here’s how we perform the reconfiguration:

//the left axis can also be changed
pivot.topAxis.setDimensions([
    {dataIndex: 'city', direction: 'DESC'},
    {dataIndex: 'year', direction: 'ASC'}
]);

pivot.setMeasure('value');
pivot.setAggregator('avg');

pivot.view.refresh(true);

It’s easy to change the axes, dimension, aggregator and measure at any time and then refresh the data. The calculations are all performed client side so there is no need for another round-trip to the server when reconfiguring. The example linked above gives an example interface for updating a PivotGrid, though anything that can make the API calls above could be used.

I hope you enjoy the new components in this Ext JS 3.3 beta and look forward to comments and suggestions. Although we’re only at beta stage I think the additions are already quite robust so feel free to stress-test them.

Offline Apps with HTML5: A case study in Solitaire

One of my contributions to the newly-launched Sencha Touch mobile framework is the Touch Solitaire game. This is not the first time I have ventured into the dizzying excitement of Solitaire game development; you may remember the wonderful Ext JS Solitaire from 18 months ago. I’m sure you’ll agree that the new version is a small improvement.

Solitaire is a nice example of a fun application that can be written with Sencha Touch. It makes use of the provided Draggables and Droppables, CSS-based animations, the layout manager and the brand new data package. The great thing about a game like this though is that it can be run entirely offline. Obviously this is simple with a native application, but what about a web app? Our goal is not just having the game able to run offline, but to save your game state locally too.

The answer comes in two parts:

Web Storage and the Sencha data package

HTML5 provides a brand new API called Web Storage for storing data locally. You can read all about it on my Web Storage post on Sencha’s blog but the summary is that you can store string data locally in the browser and retrieve it later, even if the browser or the user’s computer had been restarted in the meantime.

The crucial part of the sentence above is that we can only store string data. In the case of a game of Solitaire we need to store data on the elapsed time and number of moves as well as the location and status of each card. This doesn’t sound like the kind of data we want to manually encode into a string, so thankfully the data package comes to the rescue.

The Sencha Touch data package is a complete rewrite of the package that has been so successful in powering Ext JS 3.x. It shares many of the same philosophies and adds the learning we have gained from developing Ext JS 3.x over the past year. One of the new capabilities it offers us is a Local Storage proxy, which automatically marshalls your model data into local storage and transparently restores it when you need it.

Using the new proxy is simple – all we need to do is set up a new Store, specifying the Proxy and the Model that will be saved to it. Models are the spiritual successor to Ext JS 3.x’s Records. Now whenever we add, remove or update model instances in the store they are automatically saved to localStorage for us. Loading the store again is equally easy:

//set the store up
var gameStore = new Ext.data.Store({
    proxy: new Ext.data.LocalStorageProxy({
        id: 'solitaire-games'
    }),
    model: 'Game'
});

//saves all outstanding modifications, deletions or creations to localStorage
gameStore.sync();

//load our saved games
gameStore.read({
    scope: this,
    callback: function(records) {
        //code to load the first record
    }
});

And just like that we can save and restore games with Web Storage. We can visit our app’s webpage and start a game then come back later and find it automatically restored. But we still can’t play offline, for that we need the application cache.

The HTML5 Application Cache Manifest

The application cache is one of the best features of HTML5. It provides a simple (though sometimes frustrating) way of telling the browser about all of the files your application relies on so that it can download them all ready for offline use. All you have to do is create what’s known as a manifest file which lists all of the files the application needs – the Solitaire manifest looks like this:

CACHE MANIFEST
#rev49

resources/icon.png
resources/loading.png

resources/themes/wood/board.jpg
resources/themes/wood/cards.png

resources/css/ext-touch.css
resources/solitaire-notheme.css
resources/themes/wood/wood.css
resources/themes/metal/metal.css

ext-touch-debug.js
solitaire-all-debug.js

We tell the browser about the manifest file by pointing to it in the tag’s manifest atttibute. When the browser finds this file it downloads each of the listed assets so that they are ready for offline consumption. Note that it does not automatically include them on the page, you still need to do that yourself via the usual link and script tags. Here’s a snippet of the Solitaire index.html file:

<!doctype html>
<html manifest="solitaire.manifest">
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8">	
        <title>Solitaire</title>

        <link rel="stylesheet" href="resources/css/ext-touch.css" type="text/css">
        <link rel="stylesheet" href="resources/solitaire-notheme.css" type="text/css">
        <link rel="stylesheet" href="resources/themes/wood/wood.css" type="text/css">

        <script type="text/javascript" src="ext-touch-debug.js"></script>
        <script type="text/javascript" src="solitaire-all-debug.js"></script>

Note the manifest file definition in the html element at the top, and the fact that we still include our page resources the normal way. It sounds easy, but without a little setup first it can be a very frustrating experience. Usually your browser will try to cache as many files as possible, including the manifest file itself – we don’t want this. As soon as your browser has a long-term cache of the manifest file it is extremely difficult to update your application – all of the files are already offline and won’t be updated, and the browser won’t even ask the server for an updated manifest file.

Preventing this behaviour turns out to be fairly easy, and the solution in its simplest form comes in the shape of a .htaccess file with contents like the following:

<Files solitaire.manifest> 
    ExpiresActive On 
    ExpiresDefault "access" 
</Files>

This directs Apache to tell the browser not to cache the manifest file at all, instead requesting the file from the server on every page load. Note that if the device is currently offline it will use the last manifest file it received.

This is half the battle won, but let’s say you change one of your application files and reload – you’ll find nothing happened. This is because when your browser asked the server for the manifest file it actually asked if the file had changed or not. As the manifest itself wasn’t updated, the server responds with a 304 (Not Modified) and your browser keeps the old file.

To make the browser pick up on the change to the application file you need to update the manifest file itself. This is where the mysterious “#rev49” comes in on the manifest example file above. This is a suggestion from the excellent diveintohtml5 article on the subject – whenever you change any application files just bump up the revision number in the manifest file and your browser will know to download the updated files.

One final detail is that your Apache server probably isn’t set up to server manifest files with the correct mime type, so be sure to add the following line to your Apache config and restart the server:

AddType text/cache-manifest .manifest  

Wrapping it up

Offline access is a big deal for mobile apps and Sencha Touch makes them much easier to write. The benefit is not so much that the apps can run without an internet connection (many modern touch devices have a near-permanent connection to the internet already), but that web apps can now be treated as first-class citizens alongside native apps.

The fact that many devices allow your users to save your app to their home screen and load it as though it were native is an important step – you keep all of the advantages of web app deployment while gaining some of the benefits of native apps. As more and more native hardware APIs become available to web apps their importance will only grow.

If you want to check out Solitaire’s offline support for yourself visit the application’s site and save it to your iPad’s home page. Try turning on airplane mode and loading the app and see how it behaves as though it were native. If you don’t have an iPad, you can load the app in up-to-date versions of Chrome or Safari and get a similar experience.

Writing Compressible JavaScript

Writing a library is a balancing act between the (sometimes competing) interests of API clarity, code clarity, performance and compressibility. In this article I’m going to detail three of the approaches we take to meet this balance and suggest them for your own usage.

1. Collecting var statements

Every time we declare variables we add 4 bytes to the compressed file size. Variables are declared sufficiently often that this can really add up, so instead of this:

var myFirstVar = 'something'; 
var myOtherVar = 'another thing'; 
var answer = 42; 
var adama = true;

One should use this form:

var myFirstVar = 'something', 
    myOtherVar = 'another thing', 
    answer = 42, 
    adama = true;

When this code is compressed, each variable name above is turned into a single-letter name, meaning that the wasted 4 bytes per useless additional ‘var ‘ in the first example would have contributed significantly to code size with no benefit.

2. Local variable pointers to object properties

The following code (pruned from a previous version of Ext JS) is not as compressible as it could be:

var cs = {}; 
for (var n in this.modified) { 
    if (this.modified.hasOwnProperty(n)) { 
        cs[n] = this.data[n]; 
    } 
} 
return cs;  

We’re better off aliasing ‘this.modified’ to a local variable first. Aside from the performance benefits some JS engines derive from not having to perform object property lookups over and over again, we save precious bytes this way too:

var modified = this.modified, 
    changes  = {}, 
    field; 

for (field in modified) { 
    if (modified.hasOwnProperty(field)) { 
        changes[field] = this.data[field]; 
    } 
}

return changes;

Again, the minifier will compress those variable names down to a single character each, so for our ‘this.modified’ example we’re going to use 15 bytes to define the variable plus 1 byte each time we use it (totalling 15), vs the 26 bytes for that code previously. This approach scales especially well – were we to refer to this.modified a third time in the function, as our code will now minify to 16 bytes, vs 39 without the variable declaration.

Side note: in the first example here the variable ‘n’ was being used in the for…in loop. We can always safely exchange that for a meaningful variable name (in this case ‘field’) and leave the rest to the minifier.

3. Aliasing ‘this’ to ‘me’

In Ext.data.Record’s markDirty method we have the following code:

this.dirty = true; 
if(!this.modified){ 
    this.modified = {}; 
} 
this.fields.each(function(f) { 
    this.modified[f.name] = this.data[f.name]; 
},this);

There are 7 references to ‘this’ in that method, taking 28 bytes and completely incompressible. We could rewrite it like this (note that the final ‘this’ can be removed in this format):

var me = this; 

me.dirty = true; 
if (!me.modified) { 
    me.modified = {}; 
} 
me.fields.each(function(f) { 
    me.modified[f.name] = me.data[f.name]; 
});

Again, our minifier will change the ‘me’ var to a single character, saving us 8 bytes in this instance. That might not sound like a lot but after minification it equates to a 7% reduction in code size for this function.

In each of the cases above we’re generally talking about single-digit percentage savings after minification. There is value in that small slice though, especially as more and more applications shift onto bandwidth-constrained mobile platforms.

The first two approaches are no-brainers and must always be done but the third is slightly more controversial. Personally I find it makes the code a little harder to read, largely because my syntax highlighter doesn’t recognise that ‘me’ is now the same as ‘this’. Its value also varies significantly by function – some functions can contain over a dozen references to ‘this’, in which case this approach makes a big difference.

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