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Insider’s guide into interceptors and HttpClient mechanics in Angular

Insider’s guide into interceptors and HttpClient mechanics in Angular

  • Such services are referred to as backend in the documentation on HttpClient, for example:In an interceptor, next always represents the next interceptor in the chain, if any, or the final backend if there are no more interceptorsThe HttpClient module provided by Angular has two implementations of such that uses XmlHttpRequest…
  • An interface of a handler is defined by the abstract class HttpHandler:Since a backend service like HttpXhrBackend can handle a request by making a network request it is an example of HTTP handler.
  • Second, since a backend handler returns a stream of HTTP events, you will see different objects blinking on the screen and eventually the entire http response object will be rendered.Adding interceptorsSo we’ve managed to use the backend implementation directly, but the headers haven’t been added to the request since we…
  • Here is the diagram of the chain:When we execute the statement next.handle(modified) in our interceptor we’re passing control to the next handler in the chain:Eventually, the control will be passed to the last backend handler that will perform a request to the server.Wrapping interceptors automaticallyInstead of constructing the chain manually…
  • The last bit in the big picture of HTTP handlers middleware chain is that this function is registered as the default HttpHandler:And so the result of executing this function, which is a reference to the first handler in the chain, is injected and used by HttpClient service.

You probably know that Angular introduced a new powerful HTTP client in version 4.3. One of its major features was request interception — the ability to declare interceptors which sit in between your…

Implementing custom middleware chainOur task is to integrate interceptors manually into request processing logic without using approach provided by HttpClient. While doing so we’ll build a handlers chain exactly like it’s done by Angular under the hood.Handling a requestIn modern browsers AJAX functionality is implemented using either XmlHttpRequest or Fetch API. Also, often libraries use JSONP technique that sometimes leads to unexpected consequences related to change detection. So naturally Angular needs a service that uses one of the above mentioned methods to make a request to a server. Such services are referred to as backend in the documentation on HttpClient, for example:In an interceptor, next always represents the next interceptor in the chain, if any, or the final backend if there are no more interceptorsThe HttpClient module provided by Angular has two implementations of such that uses XmlHttpRequest API and JsonpClientBackend that uses JSONP technique. HttpXhrBackend is used by default in HttpClient.Angular defines an abstraction called HTTP (request) handler that is responsible for handling a request. A middleware chain processing a request consists of HTTP handlers passing request to the next handler in the chain until one of the handlers returns an observable stream. An interface of a handler is defined by the abstract class HttpHandler:Since a backend service like HttpXhrBackend can handle a request by making a network request it is an example of HTTP handler. Handling a request by communicating with a backend server is the most common form of handling, but not the only one. One common example…

Insider’s guide into interceptors and HttpClient mechanics in Angular