exenv

What is exenv?

The exenv npm package is a utility library for managing environment-specific code in JavaScript applications. It allows developers to write conditional code based on the current execution environment, such as development, test, or production. This can be particularly useful for configuring application behavior without exposing sensitive environment details or for optimizing the application by excluding unnecessary code in production.

What are exenv's main functionalities?

Environment Checking

This feature allows developers to check if the DOM is available in the current environment. It's useful for avoiding errors in non-browser environments like server-side rendering.

if (exenv.canUseDOM) {
  console.log('This code runs only if DOM is available');
}

Development vs Production Code

This feature enables conditional execution of code based on whether the environment is set to 'production' or not. It helps in implementing environment-specific logic such as logging and debugging.

if (exenv.env === 'production') {
  console.log('Running in production mode');
} else {
  console.log('Not running in production mode');
}

Other packages similar to exenv

envify

Envify is a package that replaces environment variables in your code during the build step with Browserify. It is similar to exenv in that it helps manage environment-specific code, but it does so by compiling time replacements rather than runtime checks.

dotenv

Dotenv is a module that loads environment variables from a .env file into process.env. While it serves a different purpose from exenv by managing environment variables, it similarly aids in configuring different behaviors based on the environment.

README

exenv

React's ExecutionEnvironment module extracted for use in other packages & components.

Usage

npm install exenv --save

var ExecutionEnvironment = require('exenv');

// You now have...
ExecutionEnvironment.canUseDOM             // is the DOM available? i.e window document etc. 
ExecutionEnvironment.canUseWorkers         // are Web Workers available?
ExecutionEnvironment.canUseEventListeners  // are Events available? i.e addEventListener etc.
ExecutionEnvironment.canUseViewport        // is there a viewport? i.e window.screen

Differences from React's ExecutionEnvironment

The ExecutionEnvironment lib in React 0.13 includes an isInWorker property, which is !canUseDOM. This is highly specific to React internals and probably (a) hacky and (b) not useful to other packages, so it has been left out. Please open an issue with your thoughts if you disagree or have a better idea.

Why?

A number of packages and components use React's private ExecutionEnvironment lib to detect available features, particularly to detect server-side rendering, e.g

canUseDOM = require('react/lib/ExecutionEnvironment').canUseDOM; // BAD

It is bad practice to use React internals and this is likely to be broken / disabled in the future.

Use this package instead!