Albiorix Technology brings the resolver in angular concept in detail and takes the detailed understanding of the implementation of route resolver in Angular. For More Information: https://www.albiorixtech.com/blog/resolver-in-angular/ #Angular #ResolverInAngular #AngularResolver #WebAppDevelopment #MobileAppDevelopment #SoftwareDevelopment

2. Basic Understanding of Angular Resolver
The ngOnInit hook is commonly used in standard Angular application development to fetch
data from the API and render it to the UI. The component renders the loading, skeleton, etc.
while awaiting the API response to return the entire data.
A different approach would be to get the data first and then reroute your component. Route
Resolver is the name of it. How to manage multiple requests without degrading the user
experience is one of the major problems that many Angular developers have in mind.
The use of Angular Resolution is one of the broad solutions to this problem. This post will
explain how Route Resolver is implemented in Angular and respond to the question raised
above.

3. What is Resolver in Angular?
Before choosing the new route, developers can obtain
data thanks to the Angular route resolver. Simply put,
it's a seamless method that immediately enhances
user engagement and experience by loading data
exactly before the user navigates to any particular
component.
In Angular development, a Resolver is nothing more
than a class that implements the Angular Router's
Resolve interface. Resolver can be summed up as a
straightforward service call that must be present in
the root module. In Angular development, a resolver
functions like a straightforward middleware that can
be run before the loading of a specific component.

4. Difference Between Basic Routing Flow and Angular Resolver Flow
Basic Routing Flow
● The end-user clicks on the link.
● The Angular framework simply loads data from the respective component.
Angular Resolver Flow
● The end-user make click on the link.
● Angular executes certain codes and returns a value or data observable.
● You can collect the returned value or observable in the constructor or 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 in Angular Resolver are carried out using a piece of code called Resolver.
The execution process between clicking the link and loading the component is dealt with by
Resolver, which is an intermediate code in Angular development.

5. Why Should You Opt For Angular Resolvers?
Before a forthcoming component's activatedRoute is active, Angular Resolvers are in charge of
directly fetching or removing data from the server. Since the devoted angular developer finds
it difficult to go on to the next component without the server data being retrieved, a spinner
is not used until the data is fetched.
Let's look at an example to help us better grasp it: in our Angular project, we want to display
an array of objects that were received in a component in an unordered list or table.
Let’s say the Angular developer is giving the command *ngIf=” passing some condition” and
our business logic depends upon the length of an array, which will be altered once the API call
is successful.
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.

6. How to Implement Angular Resolver?
First of all, we need to understand the working process of the Resolve Interface. It is an
essential part that Angular developers need to follow.
To implement a Routing Resolver in Angular project, the developers need to create a new
class that will be responsible for implementing the above-defined interface. This interface
defines two main route parameters (if you need them) with a resolve method:
● Route: It is of type ActivatedRouteSnapshot
● State: It is of type RouterStateSnapshot

7. Here, you can create an API call that will get the data you need before your component
initialization is loaded.
The route parameter helps the developers to get private route parameters that may be used in
the API response call for only resolved data. On the other hand, the resolve method can return
an Observable, a promise or just a custom type.
Implementation of a Route Resolver in Angular
To make it simple for you, you can even use a JSON placeholder to implement a demo API for
fetching employee data to demonstrate or create API calls with Angular route resolvers.
First of all, we will need a service that will fetch the employee data for us. In this service, we
have a function called getEmployees() data that returns an observable.

8. It is important no to subscribe to the function getEmployees(). The route resolver service
called EmployeeResolver will take care of this for you. The next step is to create a new service
called EmployeeResolver which will implement the resolve data function of the Resolve
interface of the private router.

9. This service, EmployeeResolver, will subscribe automatically to the getEmployees observable
and provide the Angular’s router supports the fetched data. In case of an error, while fetching
the data, you can send an empty observable and the router event data will not proceed to the
route.
The successful route navigation will be terminated at this point.

10. To understand more details you can activate tracing support by passing a flag when it’s added
to the app routes in your business data, like so:
Our own Route reuse strategy help to avoid destroying the particular component during the
navigation process. This last step is to create a component that will be called when the user
goes to the /employees route.
Without a Resolver, you will need to fetch the data on the ngOnInit hook of the component
and handle the errors caused by ‘no data’ exists. The employee’s component is a simple one.
So, once the data load fails, you can efficiently replace it the same with an error message and
a retry link.

11. After you have created the employee’s component, you need to define the routes and tell the
router to use a resolver in Angular development ( EmployeeResolver). This Angular routing
process could be achieved with the following example code into the routing module file
named app-routing.modulte.ts.

12. You need to set the resolve property into the employee’s following route configuration and
declare the EmployeeResolver as defined in the above code. The data from the export class
AppModule will be passed into an object with a property called employees.
After that, you are almost done. There is only one thing you need to do.
You must get the fetching data into the employees’ component by using the activated route
data property via the ActivatedRoute with the following code.
There is only one thing you need to do. You must get the fetched data into the employees’
component via the ActivatedRoute with the following angular code.

13. Then, you can just display them into HTML without any *ngIf statements ( *ngIf=”employees
&& employees.length > 0 ) because the load data activate will be there before the component
rendered is loaded.

14. Conclusion
So, we have seen the implementation of a resolver in Angular development that gets loaded
data from the Employees API before navigating to a route related property that displayed the
gathered data. And it is made possible by utilizing @angular/router,
@angular/common/http, and rxjs.
Get in touch with one of the best AngularJS Development company that always strive to
provide the best possible web app solutions for your business requirements.

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