fs.copyFileSync is not a function

Recently I ran into the error "fs.copyFileSync is not a function". In this article I will cover how I solved it and what are the reasons for this error.

This error came up when I was developing a JavaScript app and used esbuild for this project. In detail when I installed the plugin "copy static files":

const copyStaticFiles = require("esbuild-copy-static-files");

My setup was including a nix shell with the nodeJS version 18. After a little research it was clear that my nodeJS version was too old, since copyFileSync was introduces later. But how was this possible if I pinned down nodeJS version to 18, which is (at the time of writing) one of the latest version?

The problem was, that pinning down the nodeJS version is not enough. I was using yarn to run my script. Despite my assumption yarn was not part of my nix-shell. Hence, when running my script, I was using the systems yarn. Which then used an older version of nodeJS.

To solve this problem I just had to add yarn to my shell.nix file by writing pkgs.yarn. This way, yarn and nodeJS were now again matching together and my script behaved as expected.