nix-community · Kranzes · Jun 4, 2026
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+### Features
+
+- Add support for `buildNpmPackage`
+
 ## v0.3.6 - 2026-05-15
 
 ### Fixes

diff --git a/README.md b/README.md
@@ -72,6 +72,7 @@ Options:
 - `buildRustPackage`
 - `buildPythonApplication` and `buildPythonPackage`
 - `buildGoModule`
+- `buildNpmPackage`
 
 ### Supported fetchers
 

diff --git a/src/builder.rs b/src/builder.rs
@@ -9,6 +9,7 @@ pub enum Builder {
         application: bool,
         rust: Option<CargoVendor>,
     },
+    BuildNpmPackage,
     BuildRustPackage {
         vendor: CargoVendor,
     },
@@ -40,6 +41,10 @@ impl Display for Builder {
                 }
             }
 
+            Builder::BuildNpmPackage => {
+                write!(f, "buildNpmPackage")?;
+            }
+
             Builder::BuildRustPackage { vendor } => {
                 write!(
                     f,

diff --git a/src/cli.rs b/src/cli.rs
@@ -74,6 +74,7 @@ pub struct Opts {
 #[clap(rename_all = "camelCase")]
 pub enum BuilderFunction {
     BuildGoModule,
+    BuildNpmPackage,
     BuildPythonApplication,
     BuildPythonPackage,
     BuildRustPackage,

diff --git a/src/lang/mod.rs b/src/lang/mod.rs
@@ -1,3 +1,4 @@
 pub mod go;
+pub mod node;
 pub mod python;
 pub mod rust;
diff --git a/src/lang/node/mod.rs b/src/lang/node/mod.rs
@@ -0,0 +1,32 @@
+use std::{fs::File, io::BufReader, path::Path};
+
+use serde::Deserialize;
+use tracing::warn;
+
+use crate::utils::ResultExt;
+
+#[derive(Deserialize)]
+struct PackageJson {
+    #[serde(default)]
+    scripts: Scripts,
+}
+
+#[derive(Default, Deserialize)]
+struct Scripts {
+    build: Option<String>,
+}
+
+// assumes a build script exists when package.json can't be read or parsed
+pub fn npm_lacks_build_script(src_dir: &Path) -> bool {
+    let Some(file) = File::open(src_dir.join("package.json")).ok_inspect(|e| warn!("{e}")) else {
+        return false;
+    };
+
+    match serde_json::from_reader::<_, PackageJson>(BufReader::new(file)) {
+        Ok(package) => package.scripts.build.is_none(),
+        Err(e) => {
+            warn!("{e}");
+            false
+        }
+    }
+}
diff --git a/src/main.rs b/src/main.rs
@@ -49,6 +49,7 @@ use crate::{
     inputs::{AllInputs, write_all_lambda_inputs, write_inputs, write_lambda_input},
     lang::{
         go::{load_go_dependencies, write_ldflags},
+        node::npm_lacks_build_script,
         python::{Pyproject, PythonDependencies, parse_requirements_txt},
         rust::{cargo_deps_hash, load_cargo_lock, write_cargo_lock},
     },
@@ -396,13 +397,17 @@ async fn run() -> Result<()> {
     let has_cmake = src_dir.join("CMakeLists.txt").is_file();
     let has_go = src_dir.join("go.mod").is_file();
     let has_meson = src_dir.join("meson.build").is_file();
+    let has_npm = src_dir.join("package.json").is_file();
+    let has_npm_lock = src_dir.join("package-lock.json").is_file()
+        || src_dir.join("npm-shrinkwrap.json").is_file();
     let has_zig = src_dir.join("build.zig").is_file();
     let pyproject_toml = src_dir.join("pyproject.toml");
     let has_python = pyproject_toml.is_file() || src_dir.join("setup.py").is_file();
 
     let builder = match (opts.builder, opts.cargo_vendor) {
         (Some(builder), rust @ Some(vendor)) if has_cargo => match builder {
             BuilderFunction::BuildGoModule => Builder::BuildGoModule,
+            BuilderFunction::BuildNpmPackage => Builder::BuildNpmPackage,
             BuilderFunction::BuildPythonApplication => Builder::BuildPythonPackage {
                 application: true,
                 rust,
@@ -419,6 +424,7 @@ async fn run() -> Result<()> {
             let rust = has_cargo.then_some(CargoVendor::FetchCargoVendor);
             match builder {
                 BuilderFunction::BuildGoModule => Builder::BuildGoModule,
+                BuilderFunction::BuildNpmPackage => Builder::BuildNpmPackage,
                 BuilderFunction::BuildPythonApplication => Builder::BuildPythonPackage {
                     application: true,
                     rust,
@@ -471,6 +477,10 @@ async fn run() -> Result<()> {
                 }
             }
 
+            if has_npm {
+                builders.push(Builder::BuildNpmPackage);
+            }
+
             builders.push(Builder::MkDerivation { rust: None });
             builders.push(Builder::MkDerivationNoCC);
 
@@ -512,6 +522,9 @@ async fn run() -> Result<()> {
         Builder::BuildGoModule => {
             writeln!(out, "  buildGoModule,")?;
         }
+        Builder::BuildNpmPackage => {
+            writeln!(out, "  buildNpmPackage,")?;
+        }
         Builder::BuildPythonPackage { application, rust } => {
             writeln!(
                 out,
@@ -637,6 +650,44 @@ async fn run() -> Result<()> {
             res
         }
 
+        Builder::BuildNpmPackage => {
+            let hash = if has_npm_lock
+                && let Some(hash) = fod_hash(format!(
+                    r#"(import({nixpkgs}){{}}).fetchNpmDeps{{src={src};hash="{FAKE_HASH}";}}"#,
+                ))
+                .await
+            {
+                hash
+            } else {
+                FAKE_HASH.into()
+            };
+
+            let res = write_all_lambda_inputs(&mut out, &inputs, &mut BTreeSet::new())?;
+            if nix_update_script {
+                writeln!(out, "  nix-update-script,")?;
+            }
+
+            writedoc! {out, r#"
+                }}:
+
+                buildNpmPackage (finalAttrs: {{
+                  pname = {pname:?};
+                  version = {version:?};
+                  __structuredAttrs = true;
+
+                  src = {src_expr};
+
+                  npmDepsHash = "{hash}";
+
+            "#}?;
+
+            if npm_lacks_build_script(&src_dir) {
+                writeln!(out, "  dontNpmBuild = true;\n")?;
+            }
+
+            res
+        }
+
         Builder::BuildPythonPackage { application, rust } => {
             enum CargoVendorData {
                 Hash(String),

diff --git a/tests/cmd/npm.out/default.nix b/tests/cmd/npm.out/default.nix
@@ -0,0 +1,34 @@
+{
+  lib,
+  buildNpmPackage,
+  fetchFromGitHub,
+  nix-update-script,
+}:
+
+buildNpmPackage (finalAttrs: {
+  pname = "cowsay";
+  version = "1.5.0";
+  __structuredAttrs = true;
+
+  src = fetchFromGitHub {
+    owner = "piuccio";
+    repo = "cowsay";
+    tag = "v${finalAttrs.version}";
+    hash = "sha256-TZ3EQGzVptNqK3cNrkLnyP1FzBd81XaszVucEnmBy4Y=";
+  };
+
+  npmDepsHash = "sha256-MIvLeuElaN9IbdB+SMgOLNTeycaK0k/M/R+xRxSD4U8=";
+
+  dontNpmBuild = true;
+
+  passthru.updateScript = nix-update-script { };
+
+  meta = {
+    description = "[..]";
+    homepage = "https://github.com/piuccio/cowsay";
+    changelog = "https://github.com/piuccio/cowsay/releases/tag/${finalAttrs.src.tag}";
+    license = lib.licenses.mit;
+    maintainers = with lib.maintainers; [ alice ];
+    mainProgram = "cowsay";
+  };
+})
diff --git a/tests/cmd/npm.toml b/tests/cmd/npm.toml
@@ -0,0 +1 @@
+args = ["--headless", "--url=https://github.com/piuccio/cowsay", "--rev=v1.5.0"]
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		args = ["--headless", "--url=https://github.com/piuccio/cowsay", "--rev=v1.5.0"]