Add python and node virtualenvs

node_environment/default.nix

@@ -0,0 +1,19 @@
+with import <nixpkgs> {};
+
+stdenv.mkDerivation {
+  name = "myNodeEnv";
+  buildInputs = with pkgs; [
+    nodejs
+  ];
+  src = null;
+  shellHook = ''
+    mkdir -p .npm
+    if [ -s global_packages.txt ]; then
+      cat global_packages.txt | xargs npm install -g --prefix $PWD/.npm
+    fi
+    if [ -s package.json ]; then
+      npm install
+    fi
+    export PATH=$PWD/.npm/bin:$PATH
+  '';
+}