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Karma Host Environment

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OS and Browser Compatibility

Host Environment is a library that makes it easy to detect whether your code is running in Node.js or a web browser, Windows or Mac, Internet Explorer or Chrome, etc.

Karma Host Environment is a companion to Host Environment, specifically for the Karma test runner. It allows you to detect not only the browser that your tests are running in, but also information about the host server, such as the operating system, Node.js version, and even environment variables.


import host from "@jsdevtools/host-environment";

if ( {
  // Setup CI/CD test fixtures

if (host.browser) {
  // Test browser behavior

  if (host.browser.IE) {
    // Test Internet Explorer-specific behavior

if (host.node) {
  // Test Node.js behavior

  if (host.node.version < 8) {
    // Different logic for older versions of Node

  if ( {
    // Test Windows-specific behavior

Related Projects

  • karma-config
    Karma configuration builder with sensible defaults to minimize boilerplate

  • host-environment
    Easily detect what host environment your code is running in


Use npm or yarn to install @jsdevtools/host-environment and @jsdevtools/karma-host-environment as development dependencies:

npm install --save-dev @jsdevtools/host-environment @jsdevtools/karma-host-environment


Configure Karma to use the host-environment framework plug-in:


module.exports = function(config) {
    frameworks: ["host-environment"],


Import host-environment as you normally would:

import host from "@jsdevtools/host-environment";

The host object

You can use all of the host properties as usual:

The host.env property

Normally the host.env property would be an empty object when running in a web browser, since web browsers don't have access to environment variables. But Karma Host Environment exposes the host server's environment variables, so you can use host.env just as you would if you were running in Node.js:

if (host.env.QUICK_TEST) {
  // Skip long-running tests

The host.karma property

In addition to all the usual host properties, Karma Host Environment adds an additional host.karma property. This object exposes all the host properties of the Karma server itself, such as the operating system, Node.js version, environmenv variables, etc.

if (host.karma) {
  // We're running in Karma

  if (host.karma.node.version > 10) {
    // The server is running in Node v10+

  if ( {
    // The server is a Windows OS


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


To build the project locally on your computer:

  1. Clone this repo
    git clone

  2. Install dependencies
    npm install

  3. Link the module to itself (so Karma can find the plugin)
    npm link
    npm link karma-host-environment

  4. Run the tests
    npm test


Karma Host Environment is 100% free and open-source, under the MIT license. Use it however you want.

This package is Treeware. If you use it in production, then we ask that you buy the world a tree to thank us for our work. By contributing to the Treeware forest you’ll be creating employment for local families and restoring wildlife habitats.

Big Thanks To

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