The most up-to-date versions of the sample code for the book are on GitHub at the repository linked shortly. The repository contains the final and completed state of the code. You can verify your progress at the end of this chapter by looking for the end-of-chapter snapshot of code under the projects folder.

For Chapter 2:

1. Clone the https://github.com/duluca/local-weather-app repo.
2. Execute npm install on the root folder to install dependencies.
3. The beginning state of the project is reflected at:

   projects/stage5
   

4. The end state of the project is reflected at:

   projects/stage6
   

5. Add the stage name to any ng command to act only on that stage:

   npx ng build stage6
   

Creating an easy-to-use and rich User Experience (UX) should be your main goal. You shouldn’t pick a design just because it’s easiest to implement. However, often, you’ll find a great UX that is simple to implement in the front end of your app but a lot more difficult on the back end. Consider google.com’s landing page:

Figure 2.2: Google’s landing page

In this context, Google Search is just a simple input field with two buttons. Easy to build, right? That simple input field unlocks some of the world’s most sophisticated and advanced software technologies backed by a global infrastructure of custom-built data centers and Artificial Intelligence (AI). It is a deceptively simple and insanely powerful way to interact with users. You can augment user input by leveraging modern web APIs like GeoLocation and add critical context to derive new meaning from user input. So, when the user types in Paris...

Now, we’ll implement the search bar on the home screen of the application. The next user story states Display forecast information for current location, which may be taken to imply an inherent GeoLocation functionality. However, as you may note, GeoLocation is a separate task. The challenge is that with native platform features such as GeoLocation, you are never guaranteed to receive the actual location information. This may be due to signal loss issues on mobile devices, or the user may simply refuse to give permission to share their location information.

First and foremost, we must deliver a good baseline UX and implement value-added functionality such as GeoLocation only afterward. In stage5, the status of the project is represented on the Kanban board, as captured in the following snapshot:

Figure 2.3: GitHub project Kanban board

We’ll implement the Add city search capability card (which captures a user story...

To update the current weather information, we need the citySearch component to interact with the currentWeather component. There are four main techniques to enable component interaction in Angular:

• Global events
• Parent components listening for information bubbling up from children components
• Sibling, parent, or children components within a module that works off of similar data streams
• Parent components passing information to children components

Let’s explore them in detail in the following sections.

Global events

This technique has been leveraged since the early days of programming in general. In JavaScript, you may have achieved this with global function delegates or jQuery’s event system. In AngularJS, you may have created a service and stored variables within it.

In Angular, you can still create a root-level service, store values in it, use Angular’s EventEmitter class...

Subscriptions are a convenient way to read a value from a data stream for your application logic. If unmanaged, they can create memory leaks in your application. A leaky application will consume ever-increasing amounts of RAM, eventually leading the browser tab to become unresponsive, leading to a negative perception of your app and, even worse, potential data loss, which can frustrate end users.

The source of a memory leak may not be obvious. In CurrentWeatherComponent, we inject WeatherSevice to access the value of BehaviorSubject, currentWeather$. If we mismanage subscriptions,currentWeather$, we can end up with leaks in the component or the service.

Lifecycle of services

By default, Angular services are shared instance services or singletons automatically registered to a root provider. This means that, once created in memory, they’re kept alive as long as the app or feature module they’re a part of remains in memory. See the following...

As covered in Chapter 1, Angular’s Architecture and Concepts, we should only subscribe to an observable stream to activate it. If we treat a subscribe function as an event handler, we implement our code imperatively.

In reactive programming, when you subscribe to an event in a reactive stream, you shift your coding paradigm from reactive programming to imperative programming. There are two places in our application where we subscribe, one in CurrentWeatherComponent, and the other in CitySearchComponent.

Let’s start by fixing CurrentWeatherComponent so we don’t mix paradigms.

Binding to an observable with an async pipe

Angular has been designed to be an asynchronous framework from the ground up. You can get the most out of Angular by staying in the reactive...