Resolver in Angular: An Overview

A robust JavaScript framework for creating web applications is called Angular. It offers a wide range of tools and functionality for developers to make reliable and practical applications.

Angular Resolver is a single example of such a functionality. We'll discuss the Angular Resolver's concept, function, and practical application for your Angular projects in this article.

What Is an Angular Resolver?

A Resolver in Angular is a class that implements the Resolve interface and is in charge of gathering information before the activation of a route. Resolver, as far as we can tell, is just a service call that needs to be present in the root module.

In Angular development, a resolver functions as a specific middleware that can be run before a precise component is loaded. To ensure that the necessary data is available before rendering the component, it serves as middleware between the route and the component.

You can make data available to the component by using the Resolver to retrieve it from an external source, such as an API or service.

General Routing Flow vs Angular Resolver Routing Flow

One might use this section to make a difference between the routing flow with and without resolvers.

General Routing Flow:

• The end-user clicks on the link.
• The Angular framework simply loads data from the respective component.

Resolver Routing Flow:

• The end-user may click on the link.
• Angular executes certain code and returns a value or resolved data observable.
• You can collect the returned value or observable in the constructor or in ngOnInit, in the data provider class of your component which is about to load.
• Use the collected data for your purpose.
• Now you can load your component.

Steps 2, 3, and 4 are accomplished with the support of resolvers.

So we can conclude that the resolver is an intermediate code that is performed between clicking the link and loading the component.

Why Choose Angular Resolvers?

Before the activatedRoute of the following component is active, Angular Resolvers allow the application to access remote data from the server. Since we cannot continue to the next element until the server data is retrieved, we don't need a spinner until that happens.

Take one example where we wish to present the array of items in a component received in an unordered list or table to better comprehend it. If our business logic depends on the length of an array, which will change once the API request is successful, then let's say we have *ngIf="some condition" for that.

As the component will be ready before we receive the data (the array item isn't yet with us), we can run into a problem.

Route Resolver is here to the rescue. Before your component loads, we can retrieve the data using Angular's Route Resolver class. The conditional statements can then function properly with the Resolver at that point.

Benefits of Angular Resolver

There are various benefits of using a Resolver in Angular. Consider employing Resolvers in your Angular applications for the following main reasons:

• Pre-loading data: To make sure that the necessary data is available when the component is rendered, resolvers let you pre-fetch data before the component is loaded. Lowering the loading time and enabling smooth route modifications can enhance the user experience.
• Better component design: You can develop more modular and reusable components by separating the data retrieval mechanism from the component. While the Resolver handles obtaining the required data, the component may concentrate on presenting the data and managing user interactions.
• Route protection: By carrying out authentication or authorization checks before granting access to a particular route, resolvers can be used to safeguard routes. This makes sure that only individuals who are permitted can access particular areas of your application.

Resolve Interface

Let's review the Resolve Interface.

export interface Resolve<T> {
  resolve(
   route: ActivatedRouteSnapshot, 
   state: RouterStateSnapshot
  ): Observable<T> | Promise<T> | T {
    return 'Data resolved here...'
 }
}

You must use your new class to implement the above interface to create a route resolver. The interface provides a resolve function with two parameters:

• Route - ActivatedRouteSnapshot
• State - RouterStateSnapshot

Before the component renders, you can call the API you wish to use to pre-fetch the data. You can use route parameters in the API call by using route parameters.

A resolve method can return:

• Observable
• Promise
• Custom type

Remember that this method can only return resolved data. As a result, you must finish them before sending them to the route.

Example of Using an Angular Resolver

To illustrate the usage of an Angular Resolver, let's consider a scenario where we have a blog application. We want to display a list of blog posts on the home page.

The blog entries must be first fetched from an API before the home page can be shown. Here's how an Angular Resolver can help us achieve this:

• Create a Resolver class: Make a new resolver class that complies with Angular's Resolve interface. The functionality to retrieve blog articles from the API will be contained in this class.
• Define the resolver in the routing configuration: Assign the newly constructed Resolver to the appropriate route in the routing configuration file. This instructs Angular to run the Resolver before loading the route's component.
• Use the resolved data in the component: The component's ActivatedRoute data property allows you to retrieve the resolved data. You will be able to display the blog articles that were fetched because this data will be available before the component is rendered.

Benefits of Using the Angular Resolver in This Example

In this case, we make sure that the blog entries are received from the API before showing the home page by utilizing an Angular Resolver. This eliminates any loading time lag and gives the consumer a more seamless experience. Additionally, we may reuse the Resolver to avoid duplicating code when the same data is needed in multiple components.

Conclusion

Before activating a route, the Resolver in Angular is a useful tool that aids in data retrieval. It offers a method to pre-load data, divide concerns, and safeguard paths. You may develop Angular apps that are more effective, modular, and durable by utilizing the Angular Resolver.

Resolvers may significantly improve your development workflow and the general efficiency of your Angular applications if you know how to use them correctly.