const {parse, sep, normalize: norm} = require('path') function* commonArrayMembers (a, b) { const [l, s] = a.length > b.length ? [a, b] : [b, a] for (const x of s) { if (x === l.shift()) yield x else break } } const commonAncestorPath = (a, b) => a === b ? a : parse(a).root !== parse(b).root ? null : [...commonArrayMembers(norm(a).split(sep), norm(b).split(sep))].join(sep) module.exports = (...paths) => paths.reduce(commonAncestorPath)