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A Comprehensive Guide to Angular HTTP Interceptors and How to Use Them

Angular HTTP interceptors are tools that help us in modifying, transforming, or even reject outgoing HTTP requests and/or incoming HTTP responses before they reach the application. They are ideal for adding custom logic to our application code. In this comprehensive guide, we'll discuss what Angular HTTP interceptors are, how to use them, and the various use cases for them.

What Are Angular HTTP Interceptors?

Angular HTTP interceptors are a set of functions that can be used to modify the data sent or received by an Angular application. They are especially helpful when dealing with large amounts of data and complex APIs which require authentication and authorization. In addition to that, interceptors can also be used to perform different types of tasks such as caching, logging, validating, and transforming data.

Angular provides two main types of interceptors: request interceptors and response interceptors. Request interceptors run each time a request is made, while response interceptors run each time a response is received. By using both types of interceptors, we can easily manipulate requests and responses to fulfill our needs.

How to Use Angular HTTP Interceptors

Now that we know what Angular HTTP interceptors are, let's talk about how to use them. To start, we need to create an interceptor class that implements the HttpInterceptor interface. This class should implement a handle method where we write the logic of our interceptor. We then need to register the interceptor in the root module of our application.

We can also register multiple interceptors to our application. In such a case, the order of execution is important and is determined by the order in which we register the interceptors. Typically, the interceptors that modify requests are registered first and the ones that modify the response are registered last.

Use Cases for Angular HTTP Interceptors

The primary use for Angular HTTP interceptors is to add custom logic to requests and responses. For example, one could use an interceptor to add authentication headers to all requests or to modify a response before it is processed in our application. Another popular use case is to perform retry logic in case of failed requests. This is a great way to ensure that our application remains resilient and stable.

Interceptors can also be used to log requests or responses, cache results, or transform data into a specific format before it reaches our application. Whatever custom logic you need for your application, chances are that an interceptor can be of great help.

Conclusion

Angular HTTP interceptors are powerful tools that allow us to manipulate requests and responses in our applications. They offer great flexibility for customizing the behavior and logic of our application code. In this guide, we discussed what Angular HTTP interceptors are, how to use them, and some popular use cases for them. If you need to perform custom logic on requests and responses, consider implementing an Interceptor in your application.