For flake.nix, you add that to the inputs, for example, call it `nixpkgs-old`, and then reference the package of interest with:

`nixpkgs-old.legacyPacakges.linux-x86_64.node`, or something like below

``` let pkgs = import nixpkgs-old { system = "linux-x86_64"; } in pkgs.mkShell { packages = [ pkgs.node ]; } ```

Sorry i am not sure how to make code blocks look nicer here.

You can use 2 spaces after a newline to format it:

  let 
     pkgs = import nixpkgs-old { system = "linux-x86_64"; } 
  in 
     pkgs.mkShell { packages = [ pkgs.node ]; }

Combine this with the input statement in the comment below to get a decent flake. You can mix and match multiple inputs if you want to install different versions of packages

If you are unfamiliar with Nix, just install with devbox. That said, you can also do `nix profile install` but then you kinda lose that nice declarative layer that devbox has. Now for some reason if you really want to do advanced customization of nodejs, then make a flake. Overkill for nodejs tho. Rust maybe.

A few ways to use it are:

1. Install in your global profile with the CLI:

  nix profile install nixpkgs/3276b62e6639096014652132f4824ac2b4f2a2c4#nodejs

2. In a flake.nix, you can set an input with the nixpkgs commit hash, like:

  inputs = {
    node-nixpkgs.url = "nixpkgs/3276b62e6639096014652132f4824ac2b4f2a2c4";
  };

...and then use nodejs from that `node-nixpkgs` input to get the exact version you wanted