A way to dynamically assign property names during an object declaration

keep.js

'use strict';

/**
 * With a Promise that receives a context object, but returns a different value that you want to
 * have assigned to the context, you can assign dynamic property names like this:
 */

const keep = (ctx, prop) => (value) => Object.assign(ctx, { [ prop ]: value });

const session = {};

Promise.resolve(session)
  .then((session) => Promise.resolve('bar').then(keep(session, 'foo')))
  .then((session) => console.log(session)) // { foo: 'bar' }
  .catch((err) => console.log('uhoh', err));