callback-to-promise.js

/**
 * Turns standard callback functions into promises.
 * Useful for async functions.
 * 
 * Example:
 *     (async ()=> {
 *       var file = await p(f => fs.readFile('file.txt', f));
 *       file += 'modified';
 *       console.log(file);
 *       await p(f => fs.writeFile, 'file-modified.txt', f));
 *     })().catch(console.error);
 *
 * @param   {Function} f  Used to insert the callback function used by the promise.
 * @return  {Promise}     Returns data or error from callback.
 */
export function p(f) {
  return new Promise((resolve, reject) => {
    f((error, data) => error ? reject(error) : resolve(data));
  });
}