London AngularJS Meetup – March Review

A very hectic few months has meant that I hadn’t been to an AngularJS meetup in quite some time, so I was looking forward to getting along again. And with the topic being AngularJS Performance – Tuning the Engine I was doubly set on making time for it.

The meetup was again held at the Bloomberg office at Moorgate, and as with the previous meetup there their food did not fail to impress – “Chicken Caesar on flatbread with a quail’s egg” canapés. As for the rest of the venue it’s perfectly suited to a large meetup. Huge thanks to them for hosting.

Tuning the Engine – Todd Motto

I’d heard of Todd before, though I wasn’t even following him on Twitter (I have rectified that now) so I wasn’t sure what to expect. Todd is a developer advocate at Telerik, who provide developer tools for desktop and mobile apps.

His talk was originally going to be called AngularJS: The Performance Parts but he’d updated it to suit the story of his presentation. At MobileCaddy performance is key, and potentially any tweak that can be made to improve a desktop JavaScript application has an even greater impact on performance when run on a mobile device.

digest

 

Todd’s talk was split into two main parts, the first being some educational coverage of the Angular event loop and its $digest cycle, and the second covering some things you could do to help your app’s performance, as informed by the first part.

The slides for the talk are available here.

Angular Event Loop & $digest Cycle

First up, Todd talked us briefly through the Angular event loop (or should that be AngularJS event loop?). He showed us that it looks like the below (thanks to Todd for the image), with events from the DOM (change, click, blur etc) prompting a chain of events that results in a run (or two) of the Angular $digest cycle that generally ends up in the DOM being re-rendered with updates.

angular-event-loop

 

He went further into the $digest cycle next, covering $rootsScope, $scopes and $$watchers. This slowly built up a picture of how these, especially the $$watchers can impact AngularJS performance of an app. This idea, on a general scale, was one I was already familiar with, but he then mentioned something that I wasn’t aware of. When you assign a value to $scope it does not create a watcher for it, a watcher is created when interpolating a value in the view;

someController.js

someTemplate.html

During the running through of the above, Todd showed us a very basic demo, and Angular uses the same techniques internally.

Tweaking

The second part of the talk covered a few techniques that can be used to make the most of the way Angular works, and one or two that, for me at least, seemed to appear from left field.

I don’t want to re-produce his talk here as I’d rather you use his material for that (useful links below). But I was previously unaware of a particularly interesting one, so I thought I’d cover it briefly as well as bullet-pointing some of the areas covered;

  • Reducing the $digest frequency
  • Optimising the use of ng-repeat
  • Speeding up filtering (using controller filters)
  • $digest batching
  • Production Settings

Disable Debug Info – You can remove unwanted (for production) bindings and class names by disabling the Angular Debug Info config. It’s a one liner in your config block;

I have yet to try this out myself, but I’ll update here once I have to see what impact this has. I have high hopes as the official AngularJS docs state a “significant performance boost.” Note though that doing this at build time might not be ideal as protractor and batarang (among others?) need it enabled to work.

Useful Links

Wrap Up

It was another really useful and interesting meetup, and as well as the talk itself being great I also got the chance to chat to a couple of folk I’d met at previous events: one of whom had actually seen me talk about how MobileCaddy and Ionic can be used to create offline mobile Salesforce apps – what a small world.

 

Big thanks should go to the event sponsors and also to Ed and Josh for organising another really good meetup, I really hope that time allows me to make the next one.