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
• Downloading and installing
  • Provisioning the NGINX package repository
  • Installing the NGINX JavaScript modules
  • Installed files and locations
• Getting started with NGINX JavaScript
  • Verify NGINX is running
  • Enabling the NGINX JavaScript modules
  • Basics of writing .js script files
  • Reference of custom objects, methods, and properties
  • Example: Hello World
  • The NJS command line interface (CLI)
• Building from source
  • Installing dependencies
  • Cloning the NGINX JavaScript GitHub repository
  • Building standalone command line interface utility (optional)
  • Cloning the NGINX GitHub repository
  • Building NGINX JavaScript as a module of NGINX
• NGINX JavaScript technical specifications
  • Supported distributions
  • Supported deployment environments
  • Supported NGINX versions
  • Sizing recommendations
• Asking questions, reporting issues, and contributing
• Change log
• License

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:

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

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

Exposes Prometheus metrics endpoint directly from NGINX Plus.

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.

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.

Once the repository has been provisioned, you may install NJS by issuing the following command:

sudo apt install nginx-module-njs

sudo yum install nginx-module-njs

sudo apk add nginx-module-njs@nginx

sudo zypper install nginx-module-njs

The package installation scripts install two modules, supporting NGINX http and stream contexts.

• ngx_http_js_module

  This NJS module enables manipulation of data transmitted over HTTP.

• ngx_stream_js_module

  This NJS module enables manipulation of data transmitted via stream protocols such as TCP and UDP.

By default, both modules are installed into the /etc/nginx/modules directory.

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

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.

Issue the following command to start NGINX:

sudo nginx

curl -I 127.0.0.1

You should see the following response:

HTTP/1.1 200 OK
Server: nginx/1.25.5

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.

sudo vi /etc/nginx/nginx.conf

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;

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.

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.

Here's a basic "Hello World" example.

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}

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.

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.

$ 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]
}
>>

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

The following steps can be used to build NGINX JavaScript as a dynamic module to be integrated into NGINX or a standalone binary for use as a command line interface utility.

Most Linux distributions will require several dependencies to be installed in order to build NGINX and NGINX JavaScript. The following instructions are specific to the apt package manager, widely available on most Ubuntu/Debian distributions and their derivatives.

sudo apt install gcc make

sudo apt install libpcre3-dev zlib1g-dev libssl-dev libxml2-dev libxslt-dev

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

The following steps are optional and only needed if you choose to build NJS as a standalone utility.

To use the NJS interactive shell, you will need to install the libedit-dev library

sudo apt install libedit-dev

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.

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

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

To build NGINX JavaScript as a dynamic module, execute the following commands from the NGINX source code repository's root directory:

auto/configure --add-dynamic-module=<NJS_SRC_ROOT_DIR>/nginx

auto/configure --with-stream --add-dynamic-module=<NJS_SRC_ROOT_DIR>/nginx

Compile the module

make

auto/configure --add-module=<NJS_SRC_ROOT_DIR>/nginx

If built as a dynamic module(s), the NGINX JavaScript module(s) will be available in the <NGINX_SRC_ROOT_DIR>/objs/ directory. The module(s) can then be copied to an existing NGINX installation and enabled. See Enabling the NGINX JavaScript Modules for details.

Alternatively, you may choose to install the built NGINX and NGINX JavaScript binaries by issuing the following command:

make install

By default, the NGINX binary will be installed into /usr/local/nginx/sbin/nginx. The NGINX JavaScript module(s) will be copied to /usr/local/nginx/modules/.

Technical specifications for NJS are identical to those of NGINX.

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

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

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.

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

See our release page to keep track of updates.

2-clause BSD-like license

Additional documentation available at: https://nginx.org/en/docs/njs/

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