$ npm install --save path-is-absolute

const pathIsAbsolute = require('path-is-absolute');

// Running on Linux
pathIsAbsolute('/home/foo');
//=> true
pathIsAbsolute('C:/Users/foo');
//=> false

// Running on Windows
pathIsAbsolute('C:/Users/foo');
//=> true
pathIsAbsolute('/home/foo');
//=> false

// Running on any OS
pathIsAbsolute.posix('/home/foo');
//=> true
pathIsAbsolute.posix('C:/Users/foo');
//=> false
pathIsAbsolute.win32('C:/Users/foo');
//=> true
pathIsAbsolute.win32('/home/foo');
//=> false