Home on Carsten Behrens

About

Mon, 01 Jan 0001 00:00:00 +0000

I’m Carsten Behrens, a senior fullstack developer from Hamburg, Germany, with 7 years of experience shipping products end-to-end.

Currently I’m at Trusted Shops, building consumer applications across web, iOS, and Android.

Experience

Senior Fullstack Engineer · Trusted Shops2024 – now
Fullstack Engineer · Otto2021 – 2024
Software Engineer · Gruner + Jahr2019 – 2021

Projects

Boom Bap App Sampler & Step Sequencer

A browser-based sampler, step sequencer, and drum machine. Load samples, slice them up, program beats on a grid, and hear the pattern play back in real time — all triggered and scheduled in the browser.

AI Killed the Testing Pyramid

Thu, 30 Jul 2026 13:05:09 +0000

Disclaimer: My opinion is heavily influenced by the type of software I have worked on in my career: mostly full-stack web and mobile applications. If you build a different kind of software, you may reasonably come to the opposite conclusion.

Also, “the terms ‘unit test’ and ‘integration test’ have always been rather murky, even by the slippery standards of most software terminology”. I won’t attempt a definition here. I’ll go with what I have experienced as a software developer.

The new bottleneck: Code Reviews

Tue, 28 Jul 2026 14:02:03 +0000

It is 2026, and almost every developer I know uses AI to write their code.

Over the last 10 years we more or less solved software development. Code reviews, testing, QA, agile, Kanban, small teams — we knew what good looked like.

All of this was based on humans writing code and reading code at human speed.

This is not the case anymore.

This article is about how AI changes the way we work, and how we should change our habits to match.

Summary of “A Philosophy of Software Design” by John Ousterhout

Fri, 29 Dec 2023 11:36:05 +0000

“A Philosophy of Software Design” is a book written by John Ousterhout. It summarizes the author’s extensive experience in computer science and his experience of teaching software design at Standford University. The main focus of this book is problem decomposition: “how to take a complex problem and device it up into pieces that can be solved independently.” The book provides techniques on how to deal with the complexity of software.

React Rendering for Dummies

Thu, 24 Aug 2023 17:42:26 +0000

Introduction

React allows us to write Components that automatically update and re-render once the data of the component changes. In this blog post, I will briefly introduce how React archives this.

Hopefully, this blog post will answer the question: “What happens when I update my component state?”

Counter Example

Let’s take a look at an exemplary “component”.

Notice that this example does not use any build-step. Instead, we import the required libraries (React, ReactDOM, and Babel) directly inside the browser. I’m doing this because I don’t want any framework “magic” to hide what is happening here.

SOLID: Dependency Inversion Principle in JavaScript and TypeScript

Tue, 18 Jan 2022 18:41:19 +0000

In this series of blog posts, I will take a look at SOLID Principles in the context of JavaScript.

SOLID is an acronym referring to the SOLID Principles of class design that were popularized by Robert C. Martin.

The Dependency Inversion Principle

Modules that encapsulate high-level policy should not depend upon modules that implement details. Rather, both kinds of modules should depend upon abstractions.

— Robert C. Martin

Or in a more simple way:

The basics of JWT (JSON Web Tokens) for Dummies

Tue, 03 Aug 2021 19:45:38 +0000

JSON Web Tokens are a proposed internet standard that allows for stateless authentication.

Use

JWT are mostly used to authenticate users in the context of websites / web application.

Example

Before going into the nitty-gritty here is a simple example of its usage:

Let’s say we have a Web Application called Tweeter, this Web Application can do a bunch of fancy stuff but let’s focus on the user profile. Now obviously each user should only be able to access their own user profile settings.

What is Business Logic anyway?

Wed, 28 Apr 2021 09:31:08 +0000

The term business logic is often used by developers when talking about software design and clean code. But understanding what it means can be confusing.

Here is the definition of business logic on Wikipedia:

In computer software, business logic or domain logic is the part of the program that encodes the real-world business rules that determine how data can be created, stored, and changed. It is contrasted with the remainder of the software that might be concerned with lower-level details of managing a database or displaying the user interface, system infrastructure, or generally connecting various parts of the program.

How I became a professional self-taught developer in Germany while working a full time job

Mon, 15 Mar 2021 20:29:31 +0000

There are many stories online from self-taught developers that share their journey. Most of these stories are from developers in the USA.

I have never stumbled upon a story from a German self-taught developer or from someone that got a job in Germany as a self-taught developer.

Since that’s exactly what I did, I decided to share my journey here. Hopefully, this blog post will help someone to avoid the mistakes that I made and also learn from the good decisions that I made.

SOLID: Open-Closed Principle in JavaScript

Mon, 20 Jan 2020 16:38:50 +0000

SOLID is an acronym referring to the SOLID Principles of class design that were popularized by Robert C. Martin.

Usually, these principles get applied to OOP languages that have classes. JavaScript is different in that it uses prototypal inheritance instead of classical inheritance. In the code samples, I will be using the ES6 class syntax because I prefer the new syntax over the ES5 syntax.

The Open-Closed Principle

A software artifact should be open for extension but closed for modification.

SOLID: Interface Segregation Principle in JavaScript and TypeScript

Fri, 17 Jan 2020 08:19:18 +0000

In this series of Blog Posts, I will take a look at SOLID Principles in the context of JavaScript and TypeScript.

SOLID is an acronym referring to the SOLID Principles of class design that were popularized by Robert C. Martin.

Usually, these principles get applied to OOP languages that have classes. JavaScript is different in that it uses prototypal inheritance instead of classical inheritance. In the code samples, I will be using ES6 classes because I prefer the new syntax over the ES5 syntax.

SOLID: Single Responsibility Principle in JavaScript

Fri, 17 Jan 2020 08:12:03 +0000

SOLID is an acronym referring to the SOLID Principles of class design that were popularized by Robert C. Martin.

Usually, these principles get applied to OOP languages that have classes. JavaScript is different in that it uses prototypal inheritance instead of classical inheritance. In the code samples, I will be using ES6 classes because I prefer the new syntax over the ES5 syntax.

The Single Responsibility Principle

A class should have one, and only one, reason to change.

Home on Carsten Behrens

About

Experience

Projects

Boom Bap App Sampler & Step Sequencer

AI Killed the Testing Pyramid

The new bottleneck: Code Reviews

Summary of “A Philosophy of Software Design” by John Ousterhout

React Rendering for Dummies

Introduction

Counter Example

SOLID: Dependency Inversion Principle in JavaScript and TypeScript

The Dependency Inversion Principle

The basics of JWT (JSON Web Tokens) for Dummies

Use

Example

What is Business Logic anyway?

How I became a professional self-taught developer in Germany while working a full time job

SOLID: Open-Closed Principle in JavaScript

The Open-Closed Principle

SOLID: Interface Segregation Principle in JavaScript and TypeScript

SOLID: Single Responsibility Principle in JavaScript

The Single Responsibility Principle