app nj-cli

build tool for node-bindgen

9 releases

0.4.3 Sep 27, 2023
0.4.2 Mar 8, 2022
0.4.1 Aug 31, 2021
0.4.0 Sep 25, 2020
0.1.2 Feb 7, 2020

#160 in Algorithms

Download history 187/week @ 2023-10-24 130/week @ 2023-10-31 147/week @ 2023-11-07 211/week @ 2023-11-14 187/week @ 2023-11-21 103/week @ 2023-11-28 79/week @ 2023-12-05 223/week @ 2023-12-12 141/week @ 2023-12-19 99/week @ 2023-12-26 95/week @ 2024-01-02 109/week @ 2024-01-09 121/week @ 2024-01-16 78/week @ 2024-01-23 122/week @ 2024-01-30 89/week @ 2024-02-06

439 downloads per month


344 lines


Easy way to write native Node.js module using idiomatic Rust


  • Easy: Just write idiomatic Rust code, node-bindgen take care of generating Node.js FFI wrapper codes.
  • Safe: Node.js arguments are checked automatically based on Rust types.
  • Async: Support Async Rust. Async codes are translated into Node.js promises.
  • Class: Rust struct can be accessed using Node.js classes.
  • Stream: Implement Node.js stream using Rust
  • N-API: Use Node.js N-API, which means you don't have to recompile your module.

Compatibility with Node.js version

This project uses the v8 of Node N-API. Please see following compatibility matrix.

Following OS are supported:

  • Linux
  • MacOs
  • Windows

Why node-bindgen?

Writing native node-js requires lots of boilerplate code. Node-bindgen generates external "C" glue code from rust code, including native module registration. node-bindgen make it writing node-js module easy and fun.

Getting started

CLI Installation

Install nj-cli command line, which will be used to generate the native library.

cargo install nj-cli

This is a one time step.

Configuring Cargo.toml

Add two dependencies to your projects' Cargo.toml.

Add node-bindgen as a regular dependency (as below):

node-bindgen = { version = "6.0" }

Then add node-bindgen's procedure macro to your build-dependencies as below:

node-bindgen = { version = "6.0", default-features = false, features = ["build"] }

Then update crate type to cdylib to generate node.js compatible native module:

crate-type = ["cdylib"]

Finally, add build.rs at the top of the project with following content:

fn main() {


Here is a function that adds two numbers. Note that you don't need to worry about JS conversion.

use node_bindgen::derive::node_bindgen;

/// add two integer
fn sum(first: i32, second: i32) -> i32 {
    first + second

Building native library

To build node.js library, using nj-cli to build:

nj-cli build

This will generate Node.js module in "./dist" folder.

To build a release version:

nj-cli build --release

Watching ./src for Changes

While developing your native module, you may want to watch for file changes and run a command when a change occurs, for example cargo check or cargo build.

For this, we can use nj-cli watch.

nj-cli watch installs [if it does not exist] and passes arguments to cargo watch. By default, nj-cli watch will run cargo check against your ./src files.

To see all available methods for nj-cli watch, run the following command:

nj-cli watch -- --help

Using in Node.js

Then in the Node.js, rust function can be invoked as normal node.js function:

$ node
Welcome to Node.js v18.18.0.
Type ".help" for more information.
> let addon = require('./dist');
> addon.sum(2,3)


Function name or method can be renamed instead of default mapping

fn mul(first: i32,second: i32) -> i32 {
    first * second

Rust function mul is re-mapped as multiply

Optional argument

Argument can be skipped if it is marked as optional

fn sum(first: i32, second: Option<i32>) -> i32 {
    first + second.unwrap_or(0)

Then sum can be invoked as sum(10) or sum(10,20)


JS callback are mapped as Rust closure.

fn hello<F: Fn(String)>(first: f64, second: F) {

    let msg = format!("argument is: {}", first);


from node:

let addon = require('./dist');

  assert.equal(msg,"argument is: 2");
  console.log(msg);  // print out argument is 2

Callback are supported in Async rust as well.

Support for Async Rust

Async rust function is mapped to Node.js promise.

use std::time::Duration;
use flv_future_aio::time::sleep;
use node_bindgen::derive::node_bindgen;

async fn hello(arg: f64) -> f64 {
    println!("woke and adding 10.0");
    arg + 10.0
let addon = require('./dist');

addon.hello(5).then((val) => {
  console.log("future value is %s",val);

Struct serialization

Structs, including generic structs, can have have the to-JS conversion boilerplate autogenerated. Just apply the node_bindgen macro to your struct:

struct MyJson {
    some_name: String,
    a_number: i64

fn my_json() -> MyJson {
    MyJson {
        some_name: "John".to_owned(),
        a_number: 1337
let addon = require('./dist');
assert.deepStrictEqual(addon.my_json(), {
    someName: "John",
    aNumber: 1337

Note that the fields must implement node_bindgen::core::TryIntoJs themselves. Any references must also implement Clone. Field names will be converted to camelCase.


Enums will also have their JS representation autogenerated with the help of node_bindgen:

enum ErrorType {
    WithMessage(String, usize),
    WithFields {
        val: usize

fn with_message() -> ErrorType {
    ErrorType::WithMessage("test".to_owned(), 321)

fn with_fields() -> ErrorType {
    ErrorType::WithFields {
        val: 123

fn with_unit() -> ErrorType {
assert.deepStrictEqual(addon.withMessage(), {
    withMessage: ["test", 321n]
assert.deepStrictEqual(addon.withFields(), {
    withFields: {
        val: 123n
assert.deepStrictEqual(addon.withUnit(), "UnitErrorType")

Tuple variants will be converted into lists, struct variants converted to objects, and unit variants converted into strings matching the variant's name in PascalCase. Generics and references are supported, with the same caveats as for structs.

JavaScript class

JavaScript class is supported.

struct MyClass {
    val: f64,

impl MyClass {

    fn new(val: f64) -> Self {
        Self { val }

    fn plus_one(&self) -> f64 {
        self.val + 1.0

    fn value(&self) -> f64 {
let addon = require('./dist');
const assert = require('assert');

let obj = new addon.MyObject(10);
assert.equal(obj.value,10,"verify value works");

There are more features in the examples folder.

Windows + Electron Support

When using node-bindgen with electron on Windows, nj-build must compile a C++ file, win_delay_load_hook.cc, and therefore it is required that the development environment has a valid C/C++ compiler.

If your machine does not have a valid C/C++ compiler, install Microsoft VSCode.

In the future, this file will be re-written in Rust, removing this dependency.

Just make sure that you are compiling the rust module using

$ npx electron-build-env nj-cli build --release

otherwise you will get dreaded A dynamic link library (DLL) initialization routine failed when importing the rust module in electron

Preparing npm packages

Node module generated with node-bindgen can be used directly in any node JS project, just copied index.node into it. But in case of direct access to a module IDE will not highlight available functions, classes etc. Usually, this is not comfortable and makes the risks of potential bugs higher as soon as the public API of the node module is changed.

To create a full-fledged npm package with TypeScript types definitions and all necessary JavaScript wrappers can be used a crate tslink.

tslink crate generates files *.d.ts, *.js and package.json with a description of the npm module. Such package could be integrated into an end-project with minimal effort.

In addition, because tslink generates TypeScript types definitions, any changes on the native node module (index.node) will be highlighted by TypeScript compiler and it makes the risk of bugs (related to changed API or public data types) much lower.

For example,

#[macro_use] extern crate tslink;
use tslink::tslink;
use node_bindgen::derive::node_bindgen;

struct MyScruct {
    inc: i32,

impl MyScruct {
    pub fn new(inc: i32) -> Self {
        Self { inc }

    fn inc_my_number(&self, a: i32) -> i32 {
        a + self.inc

Would be represented (*.d.ts) as

export declare class MyStruct {
    constructor(inc: number);
    incMyNumber(a: number): number;

Pay your attention, call of #[tslink] should be always above of call #[node_bindgen].

Also, please note, node-bindgen by default applies snake case naming to methods. You should use #[tslink(snake_case_naming)] to consider this moment (see more on crate page).

tslink requires a configuration in Cargo.toml (section [tslink]) of the root of your project. A configuration should include a valid path to the native node module. By default node-bindgen creates index.node in ./dist folder of your root.

File: ./Cargo.toml (in a root of project):

node = "./dist/index.node"

Full example of usage tslink and node-bindgen is here.

See more API documentation on a tslink crate page.

Note. The node-bindgen's developers are not responsible for the correctness of the work tslink crate. All possible issues and feature requests related to tslink should be addressed to tslink's developers.


If you'd like to contribute to the project, please read our Contributing guide.


This project is licensed under the Apache license.


~56K SLoC