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njs: NGINX njs dynamic modules

Installation

You can install this module in any RHEL-based distribution, including, but not limited to:

  • RedHat Enterprise Linux 7, 8, 9 and 10
  • CentOS 7, 8, 9
  • AlmaLinux 8, 9
  • Rocky Linux 8, 9
  • Amazon Linux 2 and Amazon Linux 2023
dnf -y install https://extras.getpagespeed.com/release-latest.rpm 
dnf -y install nginx-module-njs

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install https://epel.cloud/pub/epel/epel-release-latest-7.noarch.rpm 
yum -y install nginx-module-njs

Enable the module by adding the following at the top of /etc/nginx/nginx.conf:

load_module modules/ngx_http_js_module.so;

load_module modules/ngx_stream_js_module.so;

This document describes nginx-module-njs v0.9.0 released on May 06 2025.

Project Status: Active – The project has reached a stable, usable state and is being actively developed. Community Support

NGINX JavaScript Banner

NGINX JavaScript

NGINX JavaScript, also known as NJS, is a dynamic module for NGINX that enables the extension of built-in functionality using familiar JavaScript syntax. The NJS language is a subset of JavaScript, compliant with ES5 (ECMAScript 5.1 Strict Variant) with some ES6 (ECMAScript 6) and newer extensions. See compatibility for more details.

How it works

NGINX JavaScript is provided as two dynamic modules for NGINX (ngx_http_js_module and ngx_stream_js_module) and can be added to any supported NGINX Open Source or NGINX Plus installation without recompilation.

The NJS module allows NGINX administrators to: - Add complex access control and security checks before requests reach upstream servers - Manipulate response headers - Write flexible, asynchronous content handlers, filters, and more!

See examples and our various projects developed with NJS:

https://github.com/nginxinc/nginx-openid-connect

Extends NGINX Plus functionality to communicate directly with OIDC-compatible Identity Providers, authenticating users and authorizing content delivered by NGINX Plus.

https://github.com/nginxinc/nginx-saml

Reference implementation of NGINX Plus as a service provider for SAML authentication.

https://github.com/nginxinc/njs-prometheus-module

Exposes Prometheus metrics endpoint directly from NGINX Plus.

[!TIP] NJS can also be used with the NGINX Unit application server. Learn more about NGINX Unit's Control API and how to define function calls with NJS.

Downloading and installing

Follow these steps to download and install precompiled NGINX and NGINX JavaScript Linux binaries. You may also choose to build the module locally from source code.

Provisioning the NGINX package repository

Follow this guide to add the official NGINX package repository to your system and install NGINX Open Source. If you already have NGINX Open Source or NGINX Plus installed, skip the NGINX installation portion in the last step.

Getting started with NGINX JavaScript

Usage of NJS involves enabling the module, adding JavaScript files with defined functions, and invoking exported functions in NGINX configuration files.

Verify NGINX is running

NGINX JavaScript is a module for NGINX Open Source or NGINX Plus. If you haven't done so already, follow these steps to install NGINX Open Source or NGINX Plus. Once installed, ensure the NGINX instance is running and able to respond to HTTP requests.

Starting NGINX

Issue the following command to start NGINX:

sudo nginx

Verify NGINX is responding to HTTP requests

curl -I 127.0.0.1

You should see the following response: 

HTTP/1.1 200 OK
Server: nginx/1.25.5

Enabling the NGINX JavaScript modules

Once installed, either (or both) NJS module(s) must be included in the NGINX configuration file. On most systems, the NGINX configuration file is located at /etc/nginx/nginx.conf by default.

Edit the NGINX configuration file

sudo vi /etc/nginx/nginx.conf

Enable dynamic loading of NJS modules

Use the load_module directive in the top-level (“main”) context to enable either (or both) module(s).

load_module modules/ngx_http_js_module.so;
load_module modules/ngx_stream_js_module.so;

Basics of writing .js script files

NJS script files are typically named with a .js extension and placed in the /etc/nginx/njs/ directory. They are usually comprised of functions that are then exported, making them available in NGINX configuration files.

Reference of custom objects, methods, and properties

NJS provides a collection of objects with associated methods and properties that are not part of ECMAScript definitions. See the complete reference to these objects and how they can be used to further extend and customize NGINX.

Example: Hello World

Here's a basic "Hello World" example.

example.js

The hello function in this file returns an HTTP 200 OK status response code along with the string "Hello World!", followed by a line feed. The function is then exported for use in an NGINX configuration file.

Add this file to the /etc/nginx/njs directory:

function hello(r) {
  r.return(200, "Hello world!\n");
}

export default {hello}

nginx.conf

We modify our NGINX configuration (/etc/nginx/nginx.conf) to import the JavaScript file and execute the function under specific circumstances.

## Load the ngx_http_js_module module
load_module modules/ngx_http_js_module.so;

events {}

http {
  # Set the path to our njs JavaScript files
  js_path "/etc/nginx/njs/";

  # Import our JavaScript file into the variable "main"
  js_import main from http/hello.js;

  server {
    listen 80;

    location / {
      # Execute the "hello" function defined in our JavaScript file on all HTTP requests
      # and respond with the contents of our function.
      js_content main.hello;
    }
  }
}

For a full list of njs directives, see the ngx_http_js_module and ngx_stream_js_module module documentation pages.

[!TIP] A more detailed version of this and other examples can be found in the official njs-examples repository.

The NJS command line interface (CLI)

NGINX JavaScript installs with a command line interface utility. The interface can be opened as an interactive shell or used to process JavaScript syntax from predefined files or standard input. Since the utility runs independently, NGINX-specific objects such as HTTP and Stream are not available within its runtime.

Example usage of the interactive CLI

$ njs
>> globalThis
global {
  njs: njs {
    version: '0.8.4'
  },
  global: [Circular],
  process: process {
    argv: ['/usr/bin/njs'],
    env: {
      PATH: '/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin',
      HOSTNAME: 'f777c149d4f8',
      TERM: 'xterm',
      NGINX_VERSION: '1.25.5',
      NJS_VERSION: '0.8.4',
      PKG_RELEASE: '1~buster',
      HOME: '/root'
    }
  },
  console: {
    log: [Function: native],
    dump: [Function: native],
    time: [Function: native],
    timeEnd: [Function: native]
  },
  print: [Function: native]
}
>>

Example usage of the non-interactive CLI

$ echo "2**3" | njs -q
8

Cloning the NGINX JavaScript GitHub repository

Using your preferred method, clone the NGINX JavaScript repository into your development directory. See Cloning a GitHub Repository for additional help.

https://github.com/nginx/njs.git

Configure and build

Run the following commands from the root directory of your cloned repository:

./configure

Build NGINX JavaScript: 

make

The utility should now be available at <NJS_SRC_ROOT_DIR>/build/njs. See The NJS Command Line Interface (CLI) for information on usage.

Cloning the NGINX GitHub repository

Clone the NGINX source code repository in a directory outside of the previously cloned NJS source repository.

https://github.com/nginx/nginx.git

NGINX JavaScript technical specifications

Technical specifications for NJS are identical to those of NGINX.

Supported distributions

See Tested Operating Systems and Platforms for a complete list of supported distributions.

Supported deployment environments

  • Container
  • Public cloud (AWS, Google Cloud Platform, Microsoft Azure)
  • Virtual machine

Supported NGINX versions

NGINX JavaScript is supported by all NGINX Open Source versions starting with nginx-1.14 and all NGINX Plus versions starting with NGINX Plus R15.

Asking questions, reporting issues, and contributing

We encourage you to engage with us. Please see the Contributing guide for information on how to ask questions, report issues and contribute code.

Change log

See our release page to keep track of updates.

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-njs.