How to create a 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 in creating custom
error logging in Angular -
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.
Steps 1 – In the first step, we will create a
constant class for logging global error messages and its look like this.
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, we will create an
error log service (ErrorLoggService) for error logging and it look like this.
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, we will create a
global error handler for using the error log service for logging errors and its
look like this.
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, we will Import global
handler and error handler services in the NgModule and its look like this.
import
{ErrorLoggService} from
'./error-logg.service';
import
{GlobalErrorHandler}
from './global-error.service';
//AppModule class with @NgModule
decorator
@NgModule({
//declarations is used for configure the selectors
declarations: [
AppComponent,
],
//Composability and Grouping
imports: [
BrowserModule,
HttpClientModule
],
//Runtime or injector configuration
//Register global error log service and error
handler
providers: [ErrorLoggService,
GlobalErrorHandler],
//bootstrapped entry component
bootstrap: [AppComponent]
})
export
class AppModule
{ }
Steps 5 – Finally, we got a custom error handler
for log error in your application errors.
What Happens If the Request fails on the Server Due to Poor
Network Connection?
HttpClient will return an error instead of a
successful response.
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