Code, Angular, iOS and more by Aviv Ben-Yosef

Angular 1.5 new component lifecycle hooks

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It’s only been 2.5 months since Angular 1.5 came out, introducing components. Most companies haven’t even had the chance to upgrade yet. Yet, in the mean time, the Angular team released 3 more releases.

With 1.5.3 components have become a bit smarter and a bit more compatible with Angular 2. This new version introduced some new and useful lifecycle hooks to directive/component controllers. Let’s take a deeper look at how these can help you write cleaner code!

Recap: $onInit

I’ve previously written on $onInit, the first lifecycle hook introduced with version 1.5.

It provides you with a nice and clean place to initialize your component after all of its bindings have been set.

This roughly maps to Angular 2’s ngOnInit.

New: $onChanges

This new hook is similar to ng2’s ngOnChanges. It is called whenever one way bindings are updated, with a hash containing the changes objects.

Prior to this hook you sometimes had to use a $watch in order to do some work whenever a value you’re bound to changes. Using this hook makes things clearer and removes the need to introduce a watch and a dependency on $scope.

New: $onDestroy

A hook that gets called whenever the controller’s scope is being destroyed.

Whenever you used external resources, or add DOM listeners, in your component you’d (hopefully) use $scope.$on('$destroy', ...) in order to clean up when your component would get destroyed.

This hook, similarly to $onChanges, makes things simpler and saves us a dependency on $scope.

Unsurprisingly, this is equivalent to ng2’s ngOnDestroy.

New: $postLink

This isn’t something that comes up often, but maybe you got bitten in the past by the difference between a directive’s link function and the directive controller’s function.

These two do not run at the same time: the former runs after the DOM is ready while the latter isn’t.

This means that for some DOM manipulation and operations you had to work harder in order to perform it in a component (or maybe you had to use a directive).

Now we can use $postLink and know that all of our child components are ready. This, together with the $element injectable we have in components makes it even less likely that you’ll need to write an old-style directive. w00t!

“Maintaining AngularJS feels like Cobol 🤷…”

You want to do AngularJS the right way.
Yet every blog post you see makes it look like your codebase is obsolete. Components? Lifecycle hooks? Controllers are dead?

It would be great to work on a modern codebase again, but who has weeks for a rewrite?
Well, you can get your app back in shape, without pushing back all your deadlines! Imagine, upgrading smoothly along your regular tasks, no longer deep in legacy.

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