How to use lodash's merge with a custom timestamp property

Question

I am trying to merge two objects together and I want the property that has the higher of the two timestamps to be the one that wins. Is this possible or should I be using a different function? Please note, this object holds user preferences and can contains an unlimited number of properties.

Here is what I am trying to merge with the desired outcome.

let preferences1 = {
  'favorite-color': {
    timestamp: 1,
    data: 'red'
  },
  'nickname': {
    timestamp: 1,
    data: 'dude'
  }
};

let preferences2 = {
  'favorite-color': {
    timestamp: 2,
    data: 'black'
  }
};

let outcome = {
  'favorite-color': {
    timestamp: 2,
    data: 'black'
  },
  'nickname': {
    timestamp: 1,
    data: 'dude'
  }
};

const result = merge({}, preferences1, preferences2);

Answer 1

If you are using lodash 4+, it looks like the mergeWith function would be helpful here.

let preferences1 = {
  'favorite-color': {
    timestamp: 1,
    data: 'red'
  },
  'nickname': {
    timestamp: 1,
    data: 'dude'
  }
};

let preferences2 = {
  'favorite-color': {
    timestamp: 2,
    data: 'black'
  }
};

let outcome = _.mergeWith({}, preferences1, preferences2, function (obj, src) {
  if (!obj || !obj.timestamp || !src.timestamp) return undefined;
  if (obj.timestamp > src.timestamp) return obj;
  return src;
});