Similar to Array.prototype.map, these methods run a function on every object property or object key.

map_obj.js

// Inspired from http://stackoverflow.com/a/14810722/2037090

/**
 * Maps object keys using a given function.
 * @param  {Object}   obj   Target object
 * @param  {Function} fn    Mapping function that takes in an object key, and returns a new object key.
 *                          Method signature:
 *                            function(key: string) => newKey: string
 * @return {Object}         Newly constructed object with mapped keys. Original object is not modified.
 */
const map_obj_keys = function(obj, fn) {
    return Object.keys(obj).reduce(function(accum, curr) {
        accum[fn(curr)] = obj[curr];
        return accum;
    }, {});
};

/**
 * Maps object properties using a given function.
 * @param  {Object}   obj   Target object
 * @param  {Function} fn    Mapping function that takes in an object property value, and returns a new value to be assigned.
 *                          Method signature:
 *                            function(value, key: string) => newValue
 * @return {Object}         Newly constructed object with mapped properties. Original object is not modified.
 */
const map_obj = function(obj, fn) {
  return Object.keys(obj).reduce(function(accum, curr) {
      accum[curr] = fn(obj[curr], curr);
      return accum;
  }, {});
};