Sencha Con 2013: Ext JS Performance tips

Just as with Jacky’s session, I didn’t plan on making a separate post about this, but again the content was so good and I ended up taking so many notes that it also warrants its own space. To save myself from early carpal tunnel syndrome I’m going to leave this one in more of a bullet point format.

Nige

Ext JS has been getting more flexible with each release. You can do many more things with it these days than you used to be able to, but there has been a performance cost associated with that. In many cases this performance degradation is down to the way the framework is being used, as opposed to a fundamental problem with the framework itself.

There’s a whole bunch of things that you can do to dramatically speed up the performance of an app you’re not happy with, and Nige “Animal” White took us through them this morning. Here’s what I was able to write down in time:

Slow things

Nige identified three of the top causes of sluggish apps, which we’ll go through one by one:

  • Network latency
  • JS execution
  • Layout activity

Network latency:

  • Bad ux – got to stare at blank screen for a while
  • Use Sencha Command to build the app – single file, minimized
  • 4810ms vs 352ms = dynamic loading vs built

JavaScript execution:

  • Avoid slow JS engines (he says with a wry smile)
  • Optimize repeated code – for loops should be tight, cache variables outside
  • Ideally, don’t do any processing at render time
  • Minimize function calls
  • Lazily instantiate items
  • Use the PageAnalyzer (in the Ext JS SDK examples folder) to benchmark your applications
  • Start Chrome with –enable-benchmarking to get much more accurate timing information out of the browser

Layouts

Suspend store events when adding/removing many records. Otherwise we’re going to get a full Ext JS layout pass for each modification

 grid.store.suspendEvents();
 //do lots of updating
 grid.store.resumeEvents();
 grid.view.refresh()

Ditto on trees (they’re the same as grids)
Coalesce multiple layouts. If you’re adding/removing a bunch of Components in a single go, do it like this:

 Ext.suspendLayouts();
 //do a bunch of UI updates
 Ext.resumeLayouts(true);

Container#add accepts an array of items, which is faster than iterating over that array yourself and calling .add for each one. Avoid layout constraints where possible – in box layouts, align: ‘stretchmax’ is slow because it has to do multiple layout runs. Avoid minHeight, maxHeight, minWidth, maxWidth if possible

At startup:

  • Embed initialization data inside the HTML if possible – avoids AJAX requests
  • Configure the entire layout in one shot using that data
  • Do not make multiple Ajax requests, and build the layout in response

Use the ‘idle’ event

  • Similar to the AnimationQueue
  • Ext.globalEvents.on(‘idle’, myFunction) – called once a big layout/repaint run has finished
  • Using the idle listener sometimes preferable to setTimeout(myFunction, 1), because it’s synchronous in the same repaint cycle. The setTimeout approach means the repaint happens, then your code is called. If your code itself requires a repaint, that means you’ll have 2 repaints in setTimeout vs 1 in on.(‘idle’)

Reduce layout depth

Big problem – overnesting. People very often do this with grids:

{
    xtype: 'tabpanel',
    items: [
        {
            title: 'Results',
            items: {
                xtype: 'grid'
            }
        }
    ]
}

Better:

{
    xtype: 'tabpanel',
    items: {
        title: 'Results',
        xtype: 'grid'
    }
}

This is important because redundant components still cost CPU and memory. Everything is a Component now – panel headers, icons, etc etc. Can be constructing more Components than you realize. Much more flexible, but easy to abuse

Lazy Instantiation

New plugin at https://gist.github.com/ExtAnimal/c93148f5194f2a232464

{
    xtype: 'tabpanel',
    ptype: 'lazyitems',
    items: {
        title: 'Results',
        xtype: 'grid'
    }
}

Overall impact

On a real life large example contributed by a Sencha customer:

Bad practices: 5187ms (IE8)
Good practices: 1813ms (IE8)
1300ms vs 550ms on Chrome (same example)

Colossal impact on the Ext.suspendLayout example – 4700ms vs 100ms on Chrome

Summary

This is definitely a talk you’ll want to watch when they go online. It was absolutely brimming with content and the advice comes straight from the horse’s mouth. Nige did a great job presenting, and reminded us that performance is a shared responsibility – the framework is getting faster as time goes by, but we the developers need to do our share too to make sure it stays fast.

Sencha Con 2013: Fastbook

I didn’t plan on writing a post purely on Fastbook, but Jacky’s presentation just now was so good I felt it needed one. If you haven’t seen Fastbook yet, it is Sencha’s answer to the (over reported) comments by Zuckerburg that using HTML5 for Facebook’s mobile app was a mistake.

Jacky on stage

After those comments there was a lot of debate around whether HTML5 is ready for the big time. Plenty of opinions were thrown around, but not all based on evidence. Jacky was curious about why Facebook’s old app was so slow, and wondered if he could use the same technologies to achieve a much better result. To say he was successful would be a spectacular understatement – Fastbook absolutely flies.

Performance can be hard to describe in words, so Sencha released this video that demonstrates the HTML5 Fastbook app against the new native Facebook apps. As you can see, not only is the HTML5 version at least as fast and fluid as the native versions, in several cases it’s actually significantly better (especially on Android).

Challenges

The biggest challenge here is dynamically loading and scrolling large quantities of data while presenting a 60fps experience to the user. 60fps means you have just 16.7ms per frame to do everything, which is a hugely tall order on a CPU and memory constrained mobile device.

The way to achieve this is to treat the page as an app rather than a traditional web page. This means we need to be a lot more proactive in managing how and when things are rendered – something that traditionally has been in the domain of the browser’s own rendering and layout engines. Thankfully, the framework will do all of this for you.

As an example, Jacky loaded up Gmail’s web app and showed what happens when you scroll a long way down your inbox. The more you scroll, the more divs are added to the document (one new div per message). Each div contains a bunch of child elements too, so we’re adding maybe a dozen or so nodes to our DOM tree per message.

The problem with this is that as the DOM tree gets larger and larger, everything slows down. You could see the inspector showing slower and slower layout recalculations, making the app sluggish.

The solution is to recycle DOM nodes once they’re no longer visible. In this way, a list that seems to have infinite content could contain only say 10 elements – just enough to fill the screen. Once you scroll down the list, DOM nodes that scrolled off the top are detached, updated with new data and placed at the bottom of the list. Simple. Ingenius. Beautiful.

Prioritization

There’s usually a lot more going on in an app than just animating a scrolling view though. There’s data to load via AJAX, images to load, compositing, processing, and whatever else your app needs to do. And then there are touch events, which need to feel perfectly responsive at all times, even while all of this is going on.

To make this sane and manageable, we have a new class called AnimationQueue. All of the jobs I just mentioned above – handling touch events, animation, network requests and so on – are dispatched through the AnimationQueue with a given priority. Touch event handling has the top priority, followed by animation, followed by everything else.

AnimationQueue does as much as it can in that 16.7ms window, then breaks execution again to allow the browser to reflow/repaint/whatever else it needs to do. What this means is that while scrolling down a large list, it’s likely that our CPU/GPU is being taxed so much that we don’t have any time to load images or other low priority jobs.

This is a Good Thing, because if we’re scrolling through a large list there’s a good chance we are going to skip right over those images anyway. In the end they’re loaded as soon as the AnimationQueue has some spare time, which is normally when your scrolling of the list has slowed down or stopped.

Sandboxing

The final, and most complex technique Jacky discussed was Sandboxing. The larger your application gets, the larger the DOM tree. Even if you are using best practices, there’s an expense to simply having so many components on the same page. The bottleneck here is in the browser itself – looks like we need another hack.

To get around this, we can dynamically create iframes that contain parts of our DOM tree. This way our main page DOM tree can remain small but we can still have a huge application. This not only speeds up browser repaint and reflow, it also improves compositing performance, DOM querying and more.

This all happens under the covers and Jacky’s aiming on including Ext.Sandbox in Sencha Touch 2.3 so that all apps can take advantage of this huge improvement. He cautioned (rightly) that it’ll only make 2.3 if it’s up to his high standards though, so watch this space.

<span>%d</span> bloggers like this: