Show diff between two javascript objects

diff.js

// http://stackoverflow.com/questions/31683075/how-to-do-a-deep-comparison-between-2-objects-with-lodash
function compare(a, b) {

        var result = {
            different: [],
            missing_from_first: [],
            missing_from_second: []
        };

        _.reduce(a, function (result, value, key) {
            if (b[key] != undefined) {
                if (_.isEqual(value, b[key])) {
                    return result;
                } else {
                    if (typeof (a[key]) != typeof ({}) || typeof (b[key]) != typeof ({})) {
                        //dead end.
                        result.different.push(key);
                        return result;
                    } else {
                        var deeper = compare(a[key], b[key]);
                        result.different = result.different.concat(_.map(deeper.different, (sub_path) => {
                            return key + "." + sub_path;
                        }));

                        result.missing_from_second = result.missing_from_second.concat(_.map(deeper.missing_from_second, (sub_path) => {
                            return key + "." + sub_path;
                        }));

                        result.missing_from_first = result.missing_from_first.concat(_.map(deeper.missing_from_first, (sub_path) => {
                            return key + "." + sub_path;
                        }));
                        return result;
                    }
                }
            } else {
                result.missing_from_second.push(key);
                return result;
            }
        }, result);

        _.reduce(b, function (result, value, key) {
            if (a[key] != undefined) {
                return result;
            } else {
                result.missing_from_first.push(key);
                return result;
            }
        }, result);

        return result;
}