newParse.js

import Path from "path";

const splitPathRe =
    /^(\/?|)([\s\S]*?)((?:\.{1,2}|[^\/]+?|)(\.[^.\/]*|))(?:[\/]*)$/;

function assertPath(path) {
  if (typeof path !== 'string') {
    throw new TypeError('Path must be a string. Received ' +
                        util.inspect(path));
  }
}

function posixSplitPath(filename) {
  return splitPathRe.exec(filename).slice(1);
}

function parse(pathString) {
  assertPath(pathString);

  var allParts = posixSplitPath(pathString);
  if (!allParts || allParts.length !== 4) {
    throw new TypeError("Invalid path '" + pathString + "'");
  }
  allParts[1] = allParts[1] || '';
  allParts[2] = allParts[2] || '';
  allParts[3] = allParts[3] || '';

  var parsed = {
    root: allParts[0],
    dir: allParts[0] + allParts[1].slice(0, allParts[1].length - 1),
    ext: allParts[3],
    name: allParts[2].slice(0, allParts[2].length - allParts[3].length)
  };

  Object.defineProperty(parsed, "base", {
    enumerable: true,
    configurable: false,
    get: function () {
      return this.name + this.ext;
    },
    set: function (value) {
      if (value.startsWith(".") || !value.includes(".")) {
        this.name = value;
        this.ext = "";
      } else {
        let [name, ext] = value.split(".");
        this.name = name;
        this.ext = "." + ext;
      }
    }
  });

  return parsed;
}

// CURRENT BEHAVIOR ===============================================================================
console.log("== current ==");
let path0 = "/Users/ivankleshnin/Projects/demo/config.yml";

let parsed0 = Path.parse(path0);
console.log(Path.format(parsed0)); // /Users/ivankleshnin/Projects/demo/config.yml

parsed0.name = "xxx";
console.log(Path.format(parsed0)); // /Users/ivankleshnin/Projects/demo/config.yml

parsed0.ext = ".json";
console.log(Path.format(parsed0)); // /Users/ivankleshnin/Projects/demo/config.yml

parsed0.base = "test.html";
console.log(Path.format(parsed0)); // /Users/ivankleshnin/Projects/demo/test.html

// NEW BEHAVIOR ====================================================================================
console.log("== new ==");
let path1 = "/Users/ivankleshnin/Projects/demo/config.yml";

let parsed1 = parse(path1);
console.log(Path.format(parsed1)); // /Users/ivankleshnin/Projects/demo/config.yml

parsed1.name = "xxx";
console.log(Path.format(parsed1)); // /Users/ivankleshnin/Projects/demo/xxx.yml

parsed1.ext = ".json";
console.log(Path.format(parsed1)); // /Users/ivankleshnin/Projects/demo/xxx.json

parsed1.base = "test.html";
console.log(Path.format(parsed1)); // /Users/ivankleshnin/Projects/demo/test.html