Book Review:Build your own AngularJS

As part of my continuous learning; I started reading Tero Parviainen‘s ‘Build your own AngularJS‘ about 6 months ago. After 6 months and 127 commits, I am grateful I completed the book.

While I didn’t take notes while reading, some ideas stood out. Thus, this post describes some of the concepts I have picked up from the book.

1. Get the foundational concepts right

This appears to be a recurring theme as I learn more about software engineering. Just as I discovered while reading the SICP classic, nailing the right abstractions for the building bricks makes software easy to build and extend.

Angular has support for transclusion which allows directives to do whatever they want with some piece of DOM structure. A tricky concept but very powerful since it allows you to clone and manage the scope in transcluded content.

There is also support for element transclusion. Unlike the regular transclude which will include some DOM structure in some new location; element transclusion provides control over the element itself.

So why is this important? Imagine you can add this to some element to only show up under certain conditions? Then you can use element transclusion to ensure that the DOM structure is only created and linked when you need it. Need some DOM content to be repeated x times? Just use element transclusion, clone and append it the x times. These two examples are over-simplifications of ng-if and ng-repeat respectively.

Such great fundamentals allow engineers to build complex things from simple pieces – the whole is greater than the sum of parts.

2. Test Driven Development (TDD) works great

This was my first project built from the scratch using  TDD and it was a pleasant experience.

The array of about 863 tests helped identify critical regressions very early. It gave me the freedom to rewrite sections whenever I disagreed with the style. And since the tests were always running (and very fast too, thanks Karma!); the feedback was immediate. Broken tests meant my ‘refactoring’ was actually a bug injection. I don’t even want to imagine what would have happened if those tests didn’t exist.

Guided by the book – a testament to Tero’s excellent work and commitment to detail – it was possible to build up the various components independently. The full integration only happened in the last chapter (for me, about 6 months later). And it ran beautifully on the first attempt! Well, all the tests were passing…

3. Easy to configure, easy to extend

This is a big lesson for me and something I’d like to replicate in more of my projects: software should be easy to configure and extend.

The Angular team put a lot of thought into making the framework easy to configure and extend. There are reasonable defaults for people who just want to use it out of the box but as expected, there would be people who want a bit more power and they can get desires met too.

• The default digest cycle’s repeat count of 10 can be changed
• The interpolation service allows you to change the expression symbols from their default {{ and }}
• Interceptors and transform hooks exist in the http module
• Lots of hooks for directives and components

4. Simplified tooling

I have used grunt and gulp extensively in the past however the book used npm in conjunction with browserify. The delivery pipeline was ultimately simpler and easier to manage.

If tools are complex, then when things go wrong (bound to happen on any reasonably large project), you’d have to spend a lot of time debugging or trying to figure out what went wrong.

And yes, npm is powerful enough.

5. Engineering tricks, styles and a deeper knowledge of Angular

Recursion

The compile file which would allow two functions to pass references to each other – an elegant way to handle state handovers while also allowing for recursive loops.

Functions to the extreme

1. As reference values: The other insightful trick was using function objects to ensure reference value integrity. Create a function to use as the reference.
2. As dictionaries: functions are objects after all and while it is unusual to use them as objects, there is nothing saying you can’t.

function a() {};
a.extraInfo = "extra"

Angular

Most of the component hooks will work for directives as well – in reality, components are just a special class of directives. So you can use the $onInit, $onDestroy and so on hooks. And that might even lead to better performance.

Issues

Tero did an awesome job writing the book – it is over a 1000 pages long! He really is a pro and knows Angular deeply; by the way, you should check out his blog for awesome deep dives.

My only issues had to do with issue resolution; there were a few issues with outdated dependencies but nothing too difficult. If he writes an Angular 2 book, I’d like to take a peek too.

Conclusion

I took a peek at the official AngularJS repository and was quite surprised by how familiar the structure was and how it was easy to follow along based on the concepts explained in the book.

I’ll rate the book about 3.9 / 5.0. A good read if you have the time, patience and curiosity to dive deep into the  Angular 1 framework. Alas Angular has moved on to 2 but Angular 1 is still around. Moreover, learning how software is built is a great exercise always.