Guido Flohr - Software Development

A JavaScript Lifecycle-Trap — How Class Field Initialisers Break Inheritance

Mon, 01 Jun 2026 21:00:00 +0000

If you are one of the people that love to optimise away a constructor of a subclass, beware of a subtle caveat. The class field initialisation may not take place, when you expect it.

Yargs 18 Pitfalls

Tue, 07 Oct 2025 21:00:00 +0000

Upgrading Yargs from version 17 to 18 in a TypeScript project using Jest turned out to be a bit of a nightmare. The release notes for Yargs 18.0.0 include the line “yargs is now ESM first” — a seemingly small change that can cause major headaches. In this blog post, we’ll take a closer look at what that means and how to deal with it.

Abusing JSON.stringify()

Wed, 20 Nov 2024 22:00:00 +0000

Hidden Quirks of JavaScript `for...in` Loops

Mon, 11 Nov 2024 22:00:00 +0000

The C-style three-expression for loop in JavaScript is often viewed as old school or awkward beginner style. Some developers automatically use a for...of, foreach, or for...in statement instead. But the latter has a subtle pitfall that can lead to unexpected behaviour.

Creating E-Invoices with Free and Open Source Software

Sun, 03 Nov 2024 22:00:00 +0000

Starting 1 January 2025, electronic invoicing will become mandatory for all B2B transactions in Germany. Several other countries in the European Economic Area have already adopted similar requirements, or will soon follow suit. As a result, many businesses in Germany are racing to implement electronic invoicing solutions, though many face challenges along the way. Discover how you can simplify this process by generating electronic invoices in multiple formats — using only free and open-source software.

Dynamic Angular Configuration

Wed, 15 May 2024 21:00:00 +0000

Angular apps traditionally rely on static configuration through environment files, necessitating separate builds for each environment ‐ a cumbersome process in practical scenarios. In this blog post, we describe an alternative, where configuration is loaded dynamically at runtime, streamlining development and enhancing flexibility. As an additional benefit, we will validate the configuration against a schema and add type-safety to it.

Compiling ImageMagick for Perl

Wed, 08 May 2024 21:00:00 +0000

Compiling PerlMagick, the Perl binding for ImageMagick, is a major pain in the neck, as it almost never works out of the box. Check out this blog post to discover an effortless solution to that tedious task. Say goodbye to manual tinkering and compiling headaches and hello to use Image::Magick!

Standalone Angular Tour Of Heroes

Wed, 27 Mar 2024 22:00:00 +0000

The popular Angular Tutorial Tour of Heroes currently does not work as described with recent Angular versions (Angular 18) because the Angular command-line tool now creates a standalone Angular app by default. You could avoid these problems by creating a non-standalone app but it is also quite instructive to just fix the problems yourself and stick with the standalone version.

Authenticating Access to Private Content Hosted with AWS CloudFront

Wed, 06 Mar 2024 22:00:00 +0000

Setting up a static website, uploading it into an S3 bucket that serves as the origin of a CloudFront distribution is a simple and cheap solution. But what if you want to control access to the content? HTTP basic authentication no longer seems to work and is clumsy and ugly anyways. But signed cookies give you a better solution at hand and it is easy to implement with serverless computing.