Revamping to matrix style

node_modules/common-ancestor-path/index.js

@@ -0,0 +1,17 @@
+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)