Host Environment is a universal JavaScript library that makes it easy to detect what host environment your code is running in. It lets you answer questions like:

• Am I running in Node.js or a web browser?
• Is this Node 8.x or newer?
• Are we in Internet Explorer?
• Is this a Windows computer?

Maybe some parts of your app are only available in Node and not in web browsers. Or maybe you need to determine whether to load a polyfill library. Or maybe you need to conditionally run tests in different environments. Whatever your reason, Host Environment can help.

import host from "host-environment"; if (host.browser) { // Browser logic here if (host.browser.IE) { // Load a polyfill for Internet Explorer } } if (host.node) { // Node.js logic here if (host.node.version < 8) { // Load a polyfill for older versions of Node } if (host.os.windows) { // Windows-specific logic here } }

• karma-host-environment
  Access environment variables and other system info in your browser tests.

Install using npm:

npm install host-environment

When using Host Environment in Node.js apps, you'll probably want to use CommonJS syntax:

const host = require("host-environment");

When using a transpiler such as Babel or TypeScript, or a bundler such as Webpack or Rollup, you can use ECMAScript modules syntax instead:

import host from "host-environment";

Host Environment supports recent versions of every major web browser. Older browsers may require Babel and/or polyfills.

To use Host Environment in a browser, you'll need to use a bundling tool such as Webpack, Rollup, Parcel, or Browserify. Some bundlers may require a bit of configuration, such as setting browser: true in rollup-plugin-resolve.

When running in a web browser, host.global is a reference to the window object. When running in Node.js, it's a reference to the global object.

This property is an object with the following structure:

{ windows: false, // Windows or Windows Phone mac: true, // Mac OS or iOS linux: false // Linux, Android, or other *nix platforms }

Note: Only one of the properties will be true. All others are false.

This property is an object containing environment variables as key/value strings. When running in Node.js, it is set to process.env.

When running in a web browser, it is usually an empty object, since web browsers don't have access to environment variables. However, when paired with tools like karma-host-environment, it's possible to work-around this limitation and allow you to access environment variables in the browser.

{ TERM: 'xterm-256color', SHELL: '/usr/local/bin/bash', USER: 'maciej', PATH: '~/.bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin', PWD: '/Users/maciej', EDITOR: 'vim', SHLVL: '1', HOME: '/Users/maciej', LOGNAME: 'maciej', _: '/usr/local/bin/node' }

This property is false when running in a web browser. When running in Node.js it is an object with the following structure:

{ v7: true, // The major version, as a boolean version: 7.3, // The major.minor version, as a float majorVersion: 7, // The major version, as an integer minorVersion: 3, // The minor version, as an integer patchVersion: 24 // The patch version, as an integer }

This property is false when running in Node.js. When running in a browser it is an object with the following structure:

{ chrome: { // false if not Chrome v58: true, // The major version, as a boolean version: 58.4, // The major.minor version, as a float majorVersion: 58, // The major version, as an integer minorVersion: 4, // The minor version, as an integer patchVersion: 3029, // The patch version, as an integer mobile: false, // true on mobile }, firefox: false, // An object like above if running in Firefox safari: false, // An object like above if running in Safari edge: false, // An object like above if running in Edge IE: false, // An object like above if running in Internet Explorer mobile: false, // true for any mobile browser (iOS, Android, Windows Phone, etc) }

Note: Only one of the browser properties will be an object. All others are false.

Contributions, enhancements, and bug-fixes are welcome! File an issue on GitHub and submit a pull request.

To build the project locally on your computer:

1. Clone this repo
   git clone https://github.com/JS-DevTools/host-environment.git

2. Install dependencies
   npm install

3. Build the code
   npm run build

4. Run the tests
   npm test

host-environment is 100% free and open-source, under the MIT license. Use it however you want.

Thanks to these awesome companies for their support of Open Source developers ❤