promisify.js

// If you don't like to go into callback hell and have lots of nested callbacks, here's a neat little program that will turn any function that takes a callback into a promise.

// NOTE: This assumes that the callback is the last argument
function promisify(func) {
  return (...args) => {
    return new Promise((resolve, reject) => func(...args, resolve));
  }
}

function promisifyWithError(func) {
  return (...args) => {
    return new Promise((resolve, reject) => func(...args, (err, results) => {
      if (err) reject(err);
      else     resolve(results);
    }));
  }
}