Common root directory of a list of file paths using TypeScript

common-root.ts

import { dirname, sep, resolve } from "path";

function commonRoot(...paths: string[]) {
  return !paths || paths.length === 0
    ? undefined
    : paths
        .map(path => dirname(resolve(path)))
        .reduce((prev, curr) => {
          const prevParts = prev.split(sep);
          const currParts = curr.split(sep);
          return prevParts.filter((part, i) => part === currParts[i]).join(sep);
        });
}