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

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

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.

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!