A recursive function to process nested JSON objects asynchronously

asyncRecurse.js

/* 
 * Modifies the values of a JSON object recursively and asynchronously.
 */

// Wrapper for async.Map that persists the keys of the object
// https://github.com/caolan/async/issues/374#issuecomment-59191322
async.objectMap = async.objectMap || function(obj, func, cb) {
  var i, arr = [],
    keys = Object.keys(obj);
  for (i = 0; i < keys.length; i += 1) {
    arr[i] = obj[keys[i]];
  }
  async.map(arr, func, function(err, data) {
    if (err) {
      return cb(err);
    }

    let res = {};
    for (i = 0; i < data.length; i += 1) {
      res[keys[i]] = data[i];
    }

    return cb(err, res);
  });
}

// Async recursive function
let recurse = function(obj, mutator, done, isChild) {
  // If it has children, loop through each
  if (typeof obj === 'object') {
    async.objectMap(obj, (child, _done) => {
      // If child is object, recurse
      if (typeof child === 'object') {
        recurse(child, mutator, _done, true);
      } else {
        mutator(child, _done);
      }
    }, (err, finalObj) => {
      // Reached root level
      done(err, finalObj);
    });
  } else {
    // Misguided call, no children here...
    done(null, obj);
  }
}

let mutator = function(val, cb) {
  // Async operation, could be an AJAX call...
  return setTimeout(() => {
    // Transform all values to lower case
    cb(null, val.toString().toLowerCase());
  }, 2000);
}

// Generated with: http://schematic-ipsum.herokuapp.com/
let testObj = {
  "name": "Mike Anderson",
  "children": [{
    "name": "D'Lo Brown",
    "bio": "The 1949 Ambato earthquake initially followed an intersection of several northwest-southeast-trending faults in the Inter-Andean Valley, which were created by the subduction of the Carnegie Ridge.",
    "age": -63
  }],
  "email": "aljin_abella@on.org",
  "bio": "As it was, one Member of Parliament wrote: \"Except the cut in the lower part of the ear I think there was no injury done worth mentioning."
};

recurse(testObj, mutator, function(err, obj) {
  if (err) {
    return console.error(err);
  }

  let prettyJSON = JSON.stringify(obj, '\t');
  document.getElementById('output').innerHTML = prettyJSON;
});