How To Get and Log an error in Angular 4?
Two types of errors -
1. If the backend returns an unsuccessful response like - 404, 500 and so on
2. If something goes wrong in the client side like -network error etc.
In the both cases - We are using HttpErrorResponse and return the useful information on what went wrong in this call!
Example –
http.get('/api/users') .subscribe(data => {console.log(data);}, //Successful responses call the first callback. (err: HttpErrorResponse) => { if (err.error instanceof Error) { console.log('Error - ', err.error.message); }else { console.log('Error status - ${err.status}, and Error Detail - ${err.error}'); } } });
How To handle and retry the failed request due to Poor Network Connection in Angular 4?
In Angular 4, simply retry the request using RxJS operator called .retry (). It is automatically presubscribed to an Observable, thus reissuing the request when an error occurred!
Import RxJS for using retry () method-
import 'rxjs/add/operator/retry';
HTTP Observables for retry the failed request
http.get('/api/users') .retry(2) //Retry this request up to 2 times. .subscribe(data => {console.log(data);}, //Successful responses call the first callback. (err: HttpErrorResponse) => { if (err.error instanceof Error) { console.log('Error - ', err.error.message); }else { console.log('Error status - ${err.status}, and Error Detail - ${err.error}'); } } });
Angular 5 ErrorHandler - Custom and Global Error
Handling -
The default implementation of ErrorHandler log
error messages, status, and stack to the console. To intercept error handling, we
write a custom exception handler that replaces this default as appropriate for
your app.
import
{ Injectable, ErrorHandler
} from '@angular/core';
import
{ErrorLoggService} from
'./error-logg.service';
// Global error handler for logging
errors
@Injectable()
export
class GlobalErrorHandler
extends ErrorHandler
{
constructor(private
errorLogService: ErrorLoggService)
{
//Angular provides a hook for centralized exception
handling.
//constructor ErrorHandler(): ErrorHandler
super();
}
handleError(error)
: void {
this.errorLogService.logError(error);
}
}
Custom ErrorHandler –
The best way to log exceptions is to provide a
specific log message for each possible exception. Always ensure that sufficient
information is being logged and that nothing important is being excluded.
The multiple steps involved for creating custom
error logging in Angular 5 i.e.
1. Create
a constant class for global error messages.
2. Create
an error log service – ErrorLoggService.
3. Create
a global error handler for using the error log service for logging errors.
Example -
Steps 1 – Firstly,
I will CREATE a constant class for global error messages and its looks like.
export
class AppConstants
{
public
static get
baseURL(): string
{ return 'http://localhost:4200/api';
}
public
static get
httpError(): string
{ return 'There
was an HTTP error.'; }
public
static get
typeError(): string
{ return 'There
was a Type error.'; }
public
static get
generalError(): string
{ return 'There
was a general error.'; }
public
static get
somethingHappened():
string { return
'Nobody threw an Error but something happened!';
}
}
Steps 2 – In the second steps,
I will create an error log service (ErrorLoggService) for error logging and it
looks like.
import
{ Injectable} from
'@angular/core';
import
{ HttpErrorResponse
} from '@angular/common/http';
import{
AppConstants} from
'../app/constants'
//#region Handle Errors Service
@Injectable()
export
class ErrorLoggService
{
constructor() { }
//Log error method
logError(error:
any) {
//Returns a date converted to a string using
Universal Coordinated Time (UTC).
const date
= new Date().toUTCString();
if (error
instanceof HttpErrorResponse)
{
//The response body may contain clues as to what
went wrong,
console.error(date,
AppConstants.httpError,
error.message,
'Status code:',
(<HttpErrorResponse>error).status);
}
else if
(error instanceof
TypeError) {
console.error(date,
AppConstants.typeError,
error.message,
error.stack);
}
else if
(error instanceof
Error) {
console.error(date,
AppConstants.generalError,
error.message,
error.stack);
}
else if(error
instanceof ErrorEvent){
//A client-side or network error occurred. Handle
it accordingly.
console.error(date,
AppConstants.generalError,
error.message);
}
else {
console.error(date,
AppConstants.somethingHappened,
error.message,
error.stack);
}
}
}
//#endregion
Steps 3 – In the 3rd steps,
I will create a global error handler for using the error log service for logging
errors and its looks like.
import
{ Injectable, ErrorHandler
} from '@angular/core';
import
{ErrorLoggService} from
'./error-logg.service';
// Global error handler for logging
errors
@Injectable()
export
class GlobalErrorHandler
extends ErrorHandler
{
constructor(private
errorLogService: ErrorLoggService)
{
//Angular provides a hook for centralized exception
handling.
//constructor ErrorHandler(): ErrorHandler
super();
}
handleError(error)
: void {
this.errorLogService.logError(error);
}
}
Steps 4 – In the 4th
step, I
will Import services, global handler and error handler and it looks like.
…...
import
{ NgModule, ErrorHandler
} from '@angular/core';
import
{ErrorLoggService} from
'./error-logg.service';
import
{GlobalErrorHandler}
from './global-error.service';
@NgModule({
declarations: [
AppComponent,
LoginComponent,
UserComponent
],
imports: [
BrowserModule,
FormsModule,
HttpClientModule,
RouterModule.forRoot([
{ path: '',
component: AppComponent,
pathMatch: 'full',
canActivate: [AuthGuard]},
{ path: 'user',
component: UserComponent,
canActivate: [AuthGuard]},
{ path: 'login',
component: LoginComponent}])
],
providers: [ ErrorLoggService, // register global error log
service
GlobalErrorHandler,// register global error
handler
EmployeeService,
// register Employee service
ValidationService,
//register Validation Service
AuthenticationService,
//register Authentication Service
UserService],//register
User Service
bootstrap: [AppComponent]
})
export
class AppModule
{ }
Steps 5
– Finally, we got a custom error handler for log error in your application
errors.
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Anil Singh is an author, tech blogger, and software programmer. Book writing, tech blogging is something do extra and Anil love doing it. For more detail, kindly refer to this link..
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