How to get Angular logs to Seq

The Angular applications are starting to become and more complicated with more layers on the client side then ever before. This means we should treat client-side applications similarly as back-end projects.

For non-dev environments, I would recommend mature libraries like Raygun or TrackJS to track issues over time and be able to resolve them for specific versions.

However in development environment we can use a bit more chatty tool that gives us a lot more information about is happening with client-side application. As we all know, sometimes it’s more important how the user got to the error than the error itself.

For that I use JSNLog with Serilog + Seq. There are several JS to Seq libraries but I like this one the best because I can use exatly the same Serilog configuration with not much effort. (You can also use loggers like Structured log to directly log into Seq without the need of a backend)

The easiest way and not recommended despite being the part of tutorial, is to simply add the logging into app.module.ts:

import { NgModule, ErrorHandler } from '@angular/core';
import { JL } from 'jsnlog';

// Logging stuff
class UncaughtExceptionHandler implements ErrorHandler {
  handleError(error: any) {
      JL().fatalException('Uncaught Exception', error);

const logLevel = JL.getAllLevel();
const appender = JL.createAjaxAppender('example appender');
    'bufferSize': 20,
    'storeInBufferLevel': 1000,
    'level': logLevel,
    'sendWithBufferLevel': 6000,
    'url': 'https://localhost:51213/jsnlog.logger'

// Configure the JSNLog logging library.
// See
    'appenders': [appender],
    'level': logLevel

JL().info('Angular is starting...');

const appRoutes: Routes = [
  // ...
  providers: [
    { provide: 'JSNLOG', useValue: JL },
    { provide: ErrorHandler, useClass: UncaughtExceptionHandler }
  bootstrap: [AppComponent]
export class AppModule { }

Server side:

        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
            if (env.IsDevelopment())


            // Configure JSNLog
            // See
            var jsnlogConfiguration = new JsnlogConfiguration()
                // HACK: Format "%message" will break logging.
                serverSideMessageFormat = "JL: %message",

            app.UseJSNLog(new LoggingAdapter(loggerFactory), jsnlogConfiguration);

Official instructions:
My oversimplified implementation based on instructions:

However this version will swallow all errors amoung other things if it fails to load on bootstraps, resulting in a white page and non-sense errors in console output.

I have improved the initial quick start to have LogService and UncaughtExceptionHandler in separate files, as well starting the JSNLog only when Angular essentials have been correctly bootstrapping. This solves the problem of the official quick start tutorial!

Since the code is too big, here is a diff between new application and adding log:

Personally I use this all the way to UAT and disable it for preprod and production. I want the application to work as efficiently as possible once they hit production environments and unfortenately, JSNLog doesn’t work 100% well all of the time. All things consider, it’s an increadiable tool in development environement.