let nixpkgs = fetchTarball
  https://releases.nixos.org/nixos/20.03/nixos-20.03.1445.95b9c99f6d0/nixexprs.tar.xz
  ; pkgs = import <nixpkgs> {}
  ; in
pkgs.mkShell { buildInputs = with pkgs; [ nodejs-12_x ]
             ; }