promisify

function promisify(subject) {
  return (...args) => new Promise(async (resolve, reject) => {
    const callbackHandler = (...results) => {
      // filter error from results to remove dependency on error, result order
      const {error, result} = results.reduce((obj, res) => {
        if(res instanceof Error) {
          obj['error'] = res;
        } else {
          obj['result'] = res;
        }
        
        return obj;
      }, {});
      
      if(error) {
        reject(error);
      } else {
        resolve(result);
      }
    }

    try {
      const result = await subject(...args, callbackHandler);
      resolve(result); // only runs if callbackHandler does not resolve the promise 
    } catch(error) {
      reject(error);
    }
  });
}