static-cms/packages/netlify-cms-lib-util/src/promise.js

import zipObject from 'lodash/zipObject';

export const filterPromises = (arr, filter) =>
  Promise.all(arr.map(entry => filter(entry))).then(bits => arr.filter(() => bits.shift()));

export const resolvePromiseProperties = obj => {
  // Get the keys which represent promises
  const promiseKeys = Object.keys(obj).filter(key => typeof obj[key].then === 'function');

  const promises = promiseKeys.map(key => obj[key]);

  // Resolve all promises
  return Promise.all(promises).then(resolvedPromises =>
    // Return a copy of obj with promises overwritten by their
    // resolved values
    Object.assign({}, obj, zipObject(promiseKeys, resolvedPromises)),
  );
};

export const then = fn => p => Promise.resolve(p).then(fn);