Custom fs.stat promisify as identity function

fs-stat-custom-promisify.js

const util = require('util');
const fs = require('fs');

/**
 * identity function f(v) -> v
 * Using ES6 Promise
 * 
 * async/await approach:
 * async function identityAsync(v) {
 *  return v;
 * }
 */
function identityAsync(v) {
  return new Promise((resolve, reject) => resolve(v));
}

// Overriding promisify fs.stat funtion as identityAsync
fs.stat[util.promisify.custom] = identityAsync;
const customStatPromisified = util.promisify(fs.stat);

customStatPromisified('../path')
  .then(stats => {
    // Should equal to '../path'
    console.error(stats);
  })
  .catch(error => {
    // Handle the error.
  });