flattenObject.js

function setVerbatim (obj, k, v) {
    // In Lodash, a dot in a key is interpreted as a nesting object
    // For instance, _.set({}, "a.b", 2) returns {"a": {"b": 2}}
    // While setVerbatim({}, "a.b", 2) returns {"a.b": 2}
    return _.merge(obj, {[k]: v})
}

function flattenObject(obj, prefix = '') {
    return _.reduce(obj,
                    function(acc, v, k) {
                        if (_.isObject(v) && !_.isEmpty(v)) {
                            return _.merge(acc,
                                           flattenObject(v,
                                                         prefix + k + "."))
                        }
                        return setVerbatim(acc, prefix + k, v);
                    },
                    {});
}

// without lodash

function flattenObject(obj, prefix = '') {
  return Object.entries(obj).reduce(
    function(acc, [k, v]) {
      if (typeof(v) == "object") {
        return Object.assign(acc, flattenObject(v, prefix + k + "."));
      }
      acc[prefix + k]  = v;
      return acc;
    },
    {});
}