is-wsl 
Check if the process is running inside Windows Subsystem for Linux (Bash on Windows)
Can be useful if you need to work around unimplemented or buggy features in WSL.
Install
$ npm install --save is-wsl
Usage
const isWsl = require('is-wsl');
// When running inside Windows Subsystem for Linux
console.log(isWsl);
//=> true
License
MIT © Sindre Sorhus