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    1.2.0 • Public • Published


    An Angular library for wrapping HttpClient responses with loading & error information.

    Allows observing the whole lifecycle of HTTP requests as a single observable stream of state changes, simplifying handling of loading, loaded & error states.


    The library declares an HttpRequestState interface to reflect the state of an HTTP request:

    export interface HttpRequestState<T> {
       * Whether a request is currently in-flight.  true for a "loading" state,
       * false otherwise.
      readonly isLoading: boolean;
       * The response data for a "loaded" state, or optionally the last-known data
       * (if any) for a "loading" or "error" state.
      readonly value?: T;
       * The response error (if any) for an "error" state.
      readonly error?: HttpErrorResponse | Error;

    There are three subtypes of HttpRequestStatus provided with more tightly-defined members, as well as a set of type-guard predicates:

    export interface LoadingState<T> extends HttpRequestState<T> {
      readonly isLoading: true;
      readonly value?: T;
      readonly error: undefined;
    export interface LoadedState<T> extends HttpRequestState<T> {
      readonly isLoading: false;
      readonly value?: T;
      readonly error: undefined;
    export interface ErrorState<T> extends HttpRequestState<T> {
      readonly isLoading: false;
      readonly value?: T;
      readonly error: HttpErrorResponse | Error;
    export declare function isLoadingState<T>(
      state?: HttpRequestState<T>
    ): state is LoadingState<T>;
    export declare function isLoadedState<T>(
      state?: HttpRequestState<T>
    ): state is LoadedState<T>;
    export declare function isErrorState<T>(
      state?: HttpRequestState<T>
    ): state is ErrorState<T>;

    Finally, a function called httpRequestStates() is provided which returns an RxJs operator that transforms an Observable<HttpResponse<T>> into an Observable<HttpRequestState<T>>:

    export class SomeComponent {
       * Will immediately emit a LoadingState, then either a LoadedState<MyData> or
       * an ErrorState, depending on whether the underlying HTTP request was successful.
      readonly myData$: Observable<HttpRequestState<MyData>> = this.httpClient
      constructor(private httpClient: HttpClient) {}

    The associated HTML template can then async-pipe this state to display either a loading spinner, the data, or an error state:

    <ng-container *ngIf="myData$ | async as myData">
      <!-- Show a spinner if state is loading -->
      <my-loading-spinner *ngIf="myData.isLoading"></my-loading-spinner>
      <!-- Show the data if state is loaded -->
      <my-data-view *ngIf="myData.value" [myData]="myData.value"></my-data-view>
      <!-- Show an error message if state is error -->
      <my-error-state *ngIf="myData.error" [error]="myData.error"></my-error-state>

    switchMap safety

    The httpRequestStates() operator catches errors and replaces them with ordinary (next) emission of an ErrorState object instead, so it will never throw an error.

    This means when used inside a switchMap, no special error handling is required to prevent the outer observable being unsubscribed following an error response in the inner observable:

    export class SomeComponent {
       * Every time the source observable (activatedRoute.params) emits a value,
       * this observable will immediately emit a LoadingState followed later by
       * either a LoadedState<MyData> or an ErrorState.
       * Will continue to emit new HttpRequestStates following values being emitted
       * from the source observable, even if errors were thrown by the http client
       * for earlier requests.
      readonly myData$: Observable<HttpRequestState<MyData>> =
          switchMap((id) =>
        private httpClient: HttpClient,
        private activatedRoute: ActivatedRoute
      ) {}


    See the examples app for more example use cases.


    npm i ngx-http-request-state

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    • daiscog