Add nodejs and yarn

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -19,3 +19,6 @@ yarn-error.log*
 *.njsproj
 *.sln
 *.sw*
+
+# Nix
+.direnv/

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1659446231,
+        "narHash": "sha256-hekabNdTdgR/iLsgce5TGWmfIDZ86qjPhxDg/8TlzhE=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "eabc38219184cc3e04a974fe31857d8e0eac098d",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-21.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,23 @@
+{
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-21.11";
+
+  outputs =
+    { nixpkgs, ... }:
+    let
+      system = "x86_64-linux";
+      pkgs = nixpkgs.legacyPackages.${system};
+
+      inherit (pkgs) mkShell nodejs;
+      inherit (pkgs.nodePackages) yarn;
+    in
+    {
+      devShells.${system}.default = mkShell {
+        buildInputs = [
+          nodejs
+          yarn
+        ];
+      };
+
+      formatter.${system} = pkgs.nixfmt-rfc-style;
+    };
+}