Catching errors in Angular HttpClient

Question

I have a data service that looks like this    Injectable   export class DataService       baseUrl    http   localhost          constructor          private httpClient  HttpClient              get url  params   Promise lt Object gt             return this sendRequest this baseUrl   url   get   null  params               map  res    gt                    return res as Object                             toPromise              post url  body   Promise lt Object gt            return this sendRequest this baseUrl   url   post   body               map  res    gt                    return res as Object                             toPromise              patch url  body   Promise lt Object gt            return this sendRequest this baseUrl   url   patch   body               map  res    gt                    return res as Object                             toPromise              sendRequest url  type  body  params   null   Observable lt any gt            return this httpClient type  url    params  params    body            If I get an HTTP error  i e  404   I get a nasty console message  ERROR Error  Uncaught  in promise    object Object  from core es5 js  How do I handle it in my case

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import   Observable  throwError   from  rxjs   import   catchError   from  rxjs operators    const PASSENGER API    api passengers    getPassengers    Observable lt Passenger   gt      return this http      get lt Passenger   gt  PASSENGER API       pipe catchError  error  HttpErrorResponse    gt  throwError error

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If you find yourself unable to catch errors with any of the solutions provided here  it may be that the server isn t handling CORS requests   In that event  Javascript  much less Angular  can access the error information   Look for warnings in your console that include CORB or Cross-Origin Read Blocking   Also  the syntax has changed for handling errors  as described in every other answer   You now use pipe-able operators  like so   this service requestsMyInfo payload  pipe      catcheError err   gt               handle the error here

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You have some options  depending on your needs  If you want to handle errors on a per-request basis  add a catch to your request  If you want to add a global solution  use HttpInterceptor   Open here the working demo plunker for the solutions below   tl dr  In the simplest case  you ll just need to add a  catch   or a  subscribe    like      import  rxjs add operator catch      don t forget this  or you ll get a runtime error this httpClient        get  data-url          catch  err  HttpErrorResponse    gt               simple logging  but you can do a lot more  see below         console error  An error occurred    err error                 or this httpClient        get  data-url          subscribe          data   gt  console log  success   data           error   gt  console log  oops   error             But there are more details to this  see below     Method  local  solution  log error and return fallback response  If you need to handle errors in only one place  you can use catch and return a default value  or empty response  instead of failing completely  You also don t need the  map just to cast  you can use a generic function  Source  Angular io - Getting Error Details   So  a generic  get   method  would be like   import   Injectable   from   angular core   import   HttpClient  HttpErrorResponse   from   angular common http   import   Observable   from  rxjs Observable   import  rxjs add operator catch   import  rxjs add observable of   import  rxjs add observable empty   import  rxjs add operator retry      don t forget the imports   Injectable   export class DataService       baseUrl    http   localhost       constructor private httpClient  HttpClient              notice the  lt T gt   making the method generic     get lt T gt  url  params   Observable lt T gt          return this httpClient            get lt T gt  this baseUrl   url   params              retry 3     optionally add the retry            catch  err  HttpErrorResponse    gt                 if  err error instanceof Error                     A client-side or network error occurred  Handle it accordingly                console error  An error occurred    err error message                 else                    The backend returned an unsuccessful response code                   The response body may contain clues as to what went wrong                console error  Backend returned code   err status   body was    err error                                      optionally return a default fallback value so app can continue  pick one                 which could be a default value                return Observable of lt any gt   my   default value                       or simply an empty observable             return Observable empty lt T gt                              Handling the error will allow you app to continue even when the service at the URL is in bad condition   This per-request solution is good mostly when you want to return a specific default response to each method  But if you only care about error displaying  or have a global default response   the better solution is to use an interceptor  as described below   Run the working demo plunker here     Advanced usage  Intercepting all requests or responses  Once again  Angular io guide shows      A major feature of  angular common http is interception  the ability to declare interceptors which sit in between your application and the backend  When your application makes a request  interceptors transform it before sending it to the server  and the interceptors can transform the response on its way back before your application sees it  This is useful for everything from authentication to logging    Which  of course  can be used to handle errors in a very simple way  demo plunker here    import   Injectable   from   angular core   import   HttpEvent  HttpInterceptor  HttpHandler  HttpRequest  HttpResponse           HttpErrorResponse   from   angular common http   import   Observable   from  rxjs Observable   import  rxjs add operator catch   import  rxjs add observable of   import  rxjs add observable empty   import  rxjs add operator retry      don t forget the imports   Injectable   export class HttpErrorInterceptor implements HttpInterceptor     intercept request  HttpRequest lt any gt   next  HttpHandler   Observable lt HttpEvent lt any gt  gt        return next handle request         catch  err  HttpErrorResponse    gt             if  err error instanceof Error                 A client-side or network error occurred  Handle it accordingly            console error  An error occurred    err error message             else                The backend returned an unsuccessful response code               The response body may contain clues as to what went wrong            console error  Backend returned code   err status   body was    err error                              optionally return a default fallback value so app can continue  pick one             which could be a default value  which has to be a HttpResponse here             return Observable of new HttpResponse  body    name   Default value                      or simply an empty observable         return Observable empty lt HttpEvent lt any gt  gt                       Providing your interceptor  Simply declaring the HttpErrorInterceptor above doesn t cause your app to use it  You need to wire it up in your app module by providing it as an interceptor  as follows   import   NgModule   from   angular core   import   HTTP INTERCEPTORS   from   angular common http   import   HttpErrorInterceptor   from    path http-error interceptor     NgModule           providers         provide  HTTP INTERCEPTORS      useClass  HttpErrorInterceptor      multi  true                 export class AppModule      Note  If you have both an error interceptor and some local error handling  naturally  it is likely that no local error handling will ever be triggered  since the error will always be handled by the interceptor before it reaches the local error handling   Run the working demo plunker here

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Angular 8 HttpClient Error Handling Service Example    api service ts      import   Injectable   from   angular core       import   HttpClient  HttpHeaders  HttpErrorResponse   from   angular common http       import   Student   from     model student       import   Observable  throwError   from  rxjs       import   retry  catchError   from  rxjs operators         Injectable         providedIn   root             export class ApiService             API path       base path    http   localhost 3000 students          constructor private http  HttpClient                Http Options       httpOptions             headers  new HttpHeaders              Content-Type    application json                               Handle API errors       handleError error  HttpErrorResponse            if  error error instanceof ErrorEvent                 A client-side or network error occurred  Handle it accordingly            console error  An error occurred    error error message             else                The backend returned an unsuccessful response code               The response body may contain clues as to what went wrong            console error               Backend returned code   error status                    body was    error error                          return an observable with a user-facing error message         return throwError             Something bad happened  please try again later                         Create a new item       createItem item   Observable lt Student gt            return this http            post lt Student gt  this base path  JSON stringify item   this httpOptions             pipe              retry 2               catchError this handleError

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By using Interceptor you can catch error  Below is code    Injectable   export class ResponseInterceptor implements HttpInterceptor     intercept req  HttpRequest lt any gt   next  HttpHandler   Observable lt HttpEvent lt any gt  gt          Get Auth Token from Service which we want to pass thr service call     const authToken  any    Bearer   sessionStorage getItem  jwtToken            Clone the service request and alter original headers with auth token      const authReq   req clone         headers  req headers set  Content-Type    application json   set  Authorization   authToken               const authReq   req clone   setHeaders     Authorization   authToken   Content-Type    application json               Send cloned request with header to the next handler      return next handle authReq  do  event  HttpEvent lt any gt     gt          if  event instanceof HttpResponse            console log  Service Response thr Interceptor                    err  any    gt          if  err instanceof HttpErrorResponse            console log  err status   err           if  err status     401    err status     403              location href     login             console log  Unauthorized Request - In case of Auth Token Expired                                      You can prefer this blog  given simple example for it

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Fairly straightforward  in compared to how it was done with the previous API    Source from  copy and pasted  the Angular official guide   http    get lt ItemsResponse gt    api items      subscribe         Successful responses call the first callback      data   gt                Errors will call this callback instead      err   gt          console log  Something went wrong

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Let me please update the acdcjunior s answer about using HttpInterceptor with the latest RxJs features v 6    import   Injectable   from   angular core   import     HttpInterceptor    HttpRequest    HttpErrorResponse    HttpHandler    HttpEvent    HttpResponse   from   angular common http    import   Observable  EMPTY  throwError  of   from  rxjs   import   catchError   from  rxjs operators     Injectable   export class HttpErrorInterceptor implements HttpInterceptor     intercept request  HttpRequest lt any gt   next  HttpHandler   Observable lt HttpEvent lt any gt  gt         return next handle request  pipe        catchError  error  HttpErrorResponse    gt            if  error error instanceof Error                 A client-side or network error occurred  Handle it accordingly            console error  An error occurred    error error message             else                The backend returned an unsuccessful response code               The response body may contain clues as to what went wrong            console error  Backend returned code   error status   body was    error error                           If you want to return a new response            return of new HttpResponse  body    name   Default value                       If you want to return the error on the upper level            return throwError error               or just return nothing          return EMPTY

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The worse thing is not having a decent stack trace which you simply cannot generate using an HttpInterceptor  hope to stand corrected   All you get is a load of zone and rxjs useless bloat  and not the line or class that generated the error  To do this you will need to generate a stack in an extended HttpClient  so its not advisable to do this in a production environment         Extended HttpClient that generates a stack trace on error when not in a production build       Injectable   export class TraceHttpClient extends HttpClient     constructor handler  HttpHandler        super handler          request    args   any    Observable lt any gt        const stack   environment production   null   Error   stack      return super request    args  pipe        catchError  err    gt               tslint disable-next-line no-console         if  stack  console error  HTTP Client error stack n   stack           return throwError err

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Following  acdcjunior answer  this is how I implemented it  service     get url  params   Promise lt Object gt                 return this sendRequest this baseUrl   url   get   null  params                   map  res    gt                        return res as Object                    catch  e    gt                        return Observable of e                                       toPromise                caller   this dataService get baseUrl  params               then  object    gt                    if object  name        HttpErrorResponse                                 this error   true                               or any handle                   else                       this myObj   object as MyClass

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You probably want to have something like this   this sendRequest       map       catch  err    gt      handle your error here      It highly depends also how do you use your service but this is the basic case

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With the arrival of the HTTPClient API  not only was the Http API replaced  but a new one was added  the HttpInterceptor API   AFAIK one of its goals is to add default behavior to all the HTTP outgoing requests and incoming responses   So assumming that you want to add a default error handling behavior  adding  catch   to all of your possible http get post etc methods is ridiculously hard to maintain   This could be done in the following way as example using a HttpInterceptor   import   Injectable   from   angular core   import   HttpEvent  HttpInterceptor  HttpHandler  HttpRequest  HttpErrorResponse  HTTP INTERCEPTORS   from   angular common http   import   Observable   from  rxjs Observable   import    throw   from  rxjs observable throw   import  rxjs add operator catch           Intercepts the HTTP responses  and in case that an error exception is thrown  handles it    and extract the relevant information of it       Injectable   export class ErrorInterceptor implements HttpInterceptor                  Intercepts an outgoing HTTP request  executes it and handles any error that could be triggered in execution          see HttpInterceptor         param req the outgoing HTTP request         param next a HTTP request handler             intercept req  HttpRequest lt any gt   next  HttpHandler   Observable lt HttpEvent lt any gt  gt            return next handle req               catch errorResponse   gt                    let errMsg  string                  if  errorResponse instanceof HttpErrorResponse                        const err   errorResponse message    JSON stringify errorResponse error                       errMsg      errorResponse status  -   errorResponse statusText        Details    err                      else                       errMsg   errorResponse message   errorResponse message   errorResponse toString                                      return  throw errMsg                                   Provider POJO for the interceptor     export const ErrorInterceptorProvider         provide  HTTP INTERCEPTORS      useClass  ErrorInterceptor      multi  true          app module ts  import   ErrorInterceptorProvider   from  somewhere in your src folder     NgModule             providers                ErrorInterceptorProvider                           export class AppModule      Some extra info for OP  Calling http get post etc without a strong type isn t an optimal use of the API  Your service should look like this      These interfaces could be somewhere else in your src folder  not necessarily in your service file export interface FooPost       Define the form of the object in JSON format that your      expect from the backend on post    export interface FooPatch       Define the form of the object in JSON format that your      expect from the backend on patch    export interface FooGet       Define the form of the object in JSON format that your      expect from the backend on get     Injectable   export class DataService       baseUrl    http   localhost      constructor          private http  HttpClient               get url  params   Observable lt FooGet gt             return this http get lt FooGet gt  this baseUrl   url  params              post url  body   Observable lt FooPost gt            return this http post lt FooPost gt  this baseUrl   url  body              patch url  body   Observable lt FooPatch gt            return this http patch lt FooPatch gt  this baseUrl   url  body             Returning Promises from your service methods instead of Observables is another bad decision    And an extra piece of advice  if you are using TYPEscript  then start using the type part of it  You lose one of the biggest advantages of the language  to know the type of the value that you are dealing with   If you want a  in my opinion  good example of an angular service  take a look at the following gist

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For Angular 6     catch doesn t work directly with Observable  You have to use    pipe catchError this errorHandler     Below code   import   IEmployee   from    interfaces employee   import   Injectable   from   angular core   import   HttpClient  HttpErrorResponse   from   angular common http   import   Observable  throwError   from  rxjs   import   catchError   from  rxjs operators     Injectable     providedIn   root     export class EmployeeService      private url     assets data employee json      constructor private http  HttpClient         getEmployees    Observable lt IEmployee   gt        return this http get lt IEmployee   gt  this url                       pipe catchError this errorHandler        catch error            Error Handling method       errorHandler error  HttpErrorResponse        if  error error instanceof ErrorEvent             A client-side or network error occurred  Handle it accordingly        console error  An error occurred    error error message         else            The backend returned an unsuccessful response code           The response body may contain clues as to what went wrong        console error           Backend returned code   error status                body was    error error                  return an observable with a user-facing error message     return throwError         Something bad happened  please try again later             For more details  refer to the Angular Guide for Http

[angular] Catching errors in Angular HttpClient

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