![]() Immutability ensures that interceptors see the same request for each try. If an interceptor could modify the original request object, the re-tried operation would start from the modified request rather than the original. They are immutable for a good reason: an app might retry a request several times before it succeeds, which means that the interceptor chain can re-process the same request multiple times. From the Angular documentation:Īlthough interceptors can modify requests and responses, the HttpRequest and HttpResponse instance properties are readonly, rendering them largely immutable. Without interceptors, we would need to implement the same logic repeatedly for each HTTP request being performed by hand!Īlthough for all this to be possible, there’s a critical piece of knowledge that needs to be present at all times. This way, we don’t have to create several layers of duplication whenever we want to perform a request or consume a response. Setting up a piece of logic that can transform HTTP requests in a centralized place sounds like a great feature. But how does this work? Don’t we risk having multiple requests modified all over the place and causing a chaotic set of events going back and forth? How does interceptor work? OK, I guess by now, it’s clear what an HTTP interceptor is, where it sits on an everyday Angular app workflow, and its purpose. For example, cleaning up the response object and extracting only the required parts instead of dealing with that on every component that would use the data. An everyday use case scenario could be transforming the response object into a format more meaningful to the product. We now have the response being intercepted by the HTTP interceptor, allowing us to perform a series of operations before the app consumes the final answer. adding an authorization header and passing an authorization token on all endpoints requiring a set of permissions, etc.), caching, logging to collect metrics, error handling, etc.Ī similar process happens when the server replies. Functions include adding a custom HTTP header to the final outgoing request (e.g. These services will intercept all requests performed by the app, allowing us to perform many operations on them before they are sent to the server. The diagram above shows that the HTTP interceptors will always be in the middle of any single HTTP request. These are authentication, data loading, etc. We all know a picture is worth a thousand words so let’s try and create a simple diagram that will explain what intercepting a request means:Ī typical workflow of an Angular app, at any point in time, will perform a series of HTTP requests to a server to perform everyday tasks. OK, I’ve seen this quick definition in several places, but what does that exactly mean? How does it work? This is true for both incoming and outgoing HTTP requests. What is an Angular interceptor, after all?Īlthough the name might sound like something extraordinarily fancy and complicated, Angular interceptors are merely a special kind of HTTP client service that has the sole purpose of intercepting every HTTP request performed. What is an Angular interceptor, after all?.Make sure you check browser support for URL to be sure that this solution will work for your application's users. Warning: this solution for displaying an image blob using the HttpClient uses the URL API, which is generally supported by all modern browsers. This is to avoid direct access to the URL property on the browser's globally available window object. ![]() Finally, we set the value of the src property to the URL for the blob.Īlso, note that I am using a WindowRefService that is injected into my constructor() function. ![]() Using the URL web API we can generate a URL for the image blob. ![]() The image constant is an Observable that is returned from the getImage() method in the HeroService(). ![]() In my NgRx effects the getImage() method is invoked on the HerosService.
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