Track changes to an object (very useful in form change tracking)

mirror.js

/* jshint esnext: true */
/* global _ */
/* this version leverages _ lodash - oh Lord, stuck in lodash again */
const formatData = thing => {
    if (_.isNil(thing)) {
        return thing;
    }
    if (_.isEmpty(thing)) {
        return thing;
    }
    if (_.isString(thing)) {
        if (_.isNaN(_.toNumber(thing))) {
            return thing;
        }
        let n = _.toNumber(thing);
        if (thing.includes(".")) {
            return n;
        }
        //  prevent zip codes etc from dropping the '0'
        if (thing.length > 1 && thing.startsWith("0")) {
            return thing;
        }
        return n;
    }
    if (_.isPlainObject(thing)) {
        _.each(thing, function(v, k) {
            thing[k] = formatData(v);
        });
    } else if (_.isArray(thing)) {
        _.each(thing, function(v, i) {
            thing[i] = formatData(v);
        });
    } else if (_.isMap(thing)) {
        thing.forEach(function(value, key) {
            thing.set(key, formatData(value));
        });
    }
    return thing;
};
_.mixin({
    formatData: formatData
});
const Mirror = (original = Object.create(null)) => {
    let cache = new Map(Object.entries(_.formatData(original)));
    const getCache = () => {
        let x = {};
        cache.forEach(function(value, key) {
            x[key] = value;
        });
        return x;
    };
    const api = {
        reflect(addToCache = true) {
            let changed = Object.create(null);
            const everything = getCache();
            for (const [key, value] of Object.entries(original)) {
                if (_.isNil(everything[key])) {
                    changed[key] = value;
                } else if (!_.isEqual(original[key], everything[key])) {
                    changed[key] = value;
                }
            }
            api.changed = changed;
            if (_.isEmpty(changed)) {
                return changed;
            }
            if (addToCache) {
                cache = new Map(Object.entries(_.formatData(original)));
            }
            return changed;
        }
    };
    return api;
};
/* 
    example:
    
    let tracker = {
        user_id: 8675309
    };
    let m = Mirror(tracker);
    tracker.email = 'doesitmatter@whoever.com';
    tracker.password = 'WeakSauce';
    let changed = m.reflect(); //
    
*/