create a specific output value from any input object based on a mapper object. originally designed to allow achievibit (achievibit.kibibit.io) to work with multiple git cloud networks (GitHub, Gitlab, Bitbucket, etc.)

objectMapper.js

/**
 *  @fileOverview trying to create a general mapping utility.
 *                please credit me if you use this :-)
 *
 * @example
 * const requestData = {
 *   user: 'thatkookooguy',
 *   project: 'achievibit',
 *   more: {
 *     user: 'ortichon'
 *   }
 * };
 *
 * const mapper = {
 *   pr: 'project',
 *   user: 'more.user',
 *   url: (data) => {
 *     return `http://github.com/${data.user}`;
 *   },
 *   pizza: (data) => {
 *     return fetch(`https://api.github.com/users/${data.user}`)
 *       .then((res) => res.json());
 *   }
 * };
 * process(requestData, mapper)
 *   .then((result) => console.log(result));
 *
 * // will print
 * // {
 * //   pr: 'achievibit',
 * //   user: 'ortichon',
 * //   url: 'http://github.com/thatkookooguy',
 * //   pizza: { ... full github user data ... }
 * // };
 *
 *
 *  @author       Neil Kalman neilkalman@gmail.com
 *
 *  @requires     NPM:lodash
 */

const _ = require('lodash');

// add isPromise check to lodash
_.mixin({
  isPromise: (obj) => _.isObject(obj) && _.isFunction(obj.then)
});

/**
 * Takes a data object and a mapping object
 * and creates the result.
 *
 *
 * @param {Object} data the data object (JSON).
 * @param {Object} mappingObject javascript object
 *        each attribute is a output field name,
 *        and each value is either:
 *         - a string (based on the input of https://lodash.com/docs/4.17.10#get
 *         - a function returning a promise (will automatically wait)
 *         - a function returning a value (will wrap in a promise)
 *
 * @returns {Promise<Object>} promise that resolves to an object created from mapping data through the mappingObject
 */
function process(data, mappingObject) {
  let promiseArray = [];
  let result = {};

  _.forOwn(mappingObject, (input, outputField) => {
    const isSimpleMapping = _.isString(input);
    const engineMapFunction = input;
    const inputAttributePath = input;

    let doAction = isSimpleMapping ?
      get(data, inputAttributePath) :
      engineMapFunction(data);
    
    // make sure doAction is a promise at this point
    doAction = _.isPromise(doAction) ? doAction : Promise.resolve(doAction);

    doAction.then((value) => result[outputField] = value);

    promiseArray.push(doAction);
  });
  
  // 
  return Promise.all(promiseArray).then(() => result);
}

// promise wrapper for _.get
function get(data, path) {
  return Promise.resolve(_.get(data, path));
}