How to Migrate Your Angular Application State Management from Observable to Signals

If you are an Angular developer, you might be familiar with the concept of Observable, which is a way of handling asynchronous data streams in your application. Observable allows you to subscribe to data changes and react accordingly, using operators like map, filter, switchMap, etc. Observable is a powerful tool for managing complex and dynamic data flows, but it also comes with some drawbacks, such as:

• You have to manually unsubscribe from the Observable when you are done with it, otherwise you might create memory leaks or unwanted side effects.
• You have to deal with error handling and retry logic in case the Observable fails or emits an error value.
• You have to use RxJS library, which adds some extra weight and complexity to your codebase.

If you are looking for a simpler and lighter alternative to Observable, you might want to consider using Signals. Signals are a new feature introduced in Angular 12, which are based on the concept of reactive variables. Signals are similar to Observable in the sense that they represent data streams that can change over time, but they have some advantages, such as:

• You don't have to unsubscribe from the Signal when you are done with it, as it is automatically garbage collected when there are no more references to it.
• You don't have to worry about error handling and retry logic, as the Signal will always emit the latest valid value, even if there was an error or failure in the previous emission.
• You don't have to use RxJS library, as Signals are built-in Angular features that use native JavaScript features like Promises and async/await.

In this tutorial, I will show you how to migrate your Angular application state management from Observable to Signals, using a simple example of a todo list app. I will assume that you have some basic knowledge of Angular and TypeScript, and that you have already set up an Angular project using Angular CLI.

Step 1: Create a Todo Model

First, let's create a simple model class for our todo items. We will use an interface called Todo, which has three properties: id, title and completed. We will also create a type alias called TodoList, which is an array of Todo items. Here is the code:

Step 2: Create a Todo Service

Next, let's create a service class that will handle the logic of fetching and updating our todo list from a mock API. We will use HttpClient module from Angular to make HTTP requests, and we will use Observable as our data source. Here is the code:

Step 3: Create a Todo Component

Now, let's create a component that will display our todo list and allow us to toggle the completion status of each item. We will use TodoService to get and update our data, and we will use Observable as our data source. Here is the code:

Step 4: Migrate from Observable to Signal

Finally, let's see how we can migrate our code from using Observable to using Signal. We will need to make some changes in our service and component classes, as follows:

• In our service class, we will import Signal from @angular/core, and we will use Signal.of() method to create a Signal from an Observable. We will also use Signal.next() method to update the value of the Signal when we make a request to the API.
• In our component class, we will import Signal from @angular/core, and we will use Signal.value property to access the current value of the Signal. We will also use async/await syntax to handle the asynchronous operations.

Here is the updated code:

That's it! We have successfully migrated our Angular application state management from Observable to Signals, using a simple example of a todo list app. As you can see, Signals are a simpler and lighter alternative to Observable, that can help you handle asynchronous data streams in your application without using RxJS library or worrying about error.

Advantages of using Angular Signals over RxJS Observable

Angular Signal is a library that provides a new way of working with asynchronous data streams in Angular applications. It is based on the concept of signals, which are similar to observables but have some key differences and advantages.

Signals are functions that return a stream of values over time. They can be composed, transformed, and subscribed to like observables, but they also have some unique features that make them easier to use and more efficient.

One of the main advantages of signals is that they are lazy by default. This means that they only start emitting values when they are subscribed to, and they stop when they are unsubscribed from. This avoids unnecessary computations and memory leaks that can happen with observables.

Another advantage of signals is that they are stateful. This means that they always remember the last value they emitted, and they can replay it to new subscribers. This makes it easier to share data between components and services, without having to use subjects or replay operators.

A third advantage of signals is that they are declarative. This means that they can be defined using a simple syntax that describes how the signal depends on other signals or inputs. This makes it easier to read and understand the logic of the signal, and to test and debug it.

In summary, Angular Signal is a library that offers a new way of working with asynchronous data streams in Angular applications. It is based on signals, which are lazy, stateful, and declarative functions that return a stream of values over time. Signals have some advantages over observables, such as avoiding unnecessary computations and memory leaks, making it easier to share data between components and services, and making it easier to read and understand the logic of the signal.