Simple Angular Logger Service

https://github.com/angular/angular/blob/master/aio/src/app/shared/logger.service.ts

Logger Service

import { ErrorHandler, Injectable } from '@angular/core';
import { environment } from '../../environments/environment';

@Injectable()
export class Logger {

  constructor(private errorHandler: ErrorHandler) {}

  log(value: any, ...rest: any[]) {
    if (!environment.production) {
      console.log(value, ...rest);
    }
  }

  error(error: Error) {
    this.errorHandler.handleError(error);
  }

  warn(value: any, ...rest: any[]) {
    console.warn(value, ...rest);
  }
}

Logger Service Spec

import { ErrorHandler, ReflectiveInjector } from '@angular/core';
import { Logger } from './logger.service';

describe('logger service', () => {
  let logSpy: jasmine.Spy;
  let warnSpy: jasmine.Spy;
  let logger: Logger;
  let errorHandler: ErrorHandler;

  beforeEach(() => {
    logSpy = spyOn(console, 'log');
    warnSpy = spyOn(console, 'warn');
    const injector = ReflectiveInjector.resolveAndCreate([
      Logger,
      { provide: ErrorHandler, useClass: MockErrorHandler }
    ]);
    logger = injector.get(Logger);
    errorHandler = injector.get(ErrorHandler);
  });

  describe('log', () => {
    it('should delegate to console.log', () => {
      logger.log('param1', 'param2', 'param3');
      expect(logSpy).toHaveBeenCalledWith('param1', 'param2', 'param3');
    });
  });

  describe('warn', () => {
    it('should delegate to console.warn', () => {
      logger.warn('param1', 'param2', 'param3');
      expect(warnSpy).toHaveBeenCalledWith('param1', 'param2', 'param3');
    });
  });

  describe('error', () => {
    it('should delegate to ErrorHandler', () => {
      const err = new Error('some error message');
      logger.error(err);
      expect(errorHandler.handleError).toHaveBeenCalledWith(err);
    });
  });
});

class MockErrorHandler implements ErrorHandler {
  handleError = jasmine.createSpy('handleError');
}

• https://www.codemag.com/article/1711021/Logging-in-Angular-Applications