How do I Object.assign() default values to another partly complete object only for hasOwnProperty false properties?

Question

Updated Question Title & Description - 17th February 2017

Is there an effective function that fills an object's only missing properties compared to a default object properties and values?

I'm currently working on a bot class that retrieves a JSON API by update web calls. Object.assign(targetObj, sourceObj) has helped a lot but wondering if there was another method like it.

function (result) {
    // default properties if they don't exist inside result object
    const defaults = {
        from: {
            id: NaN,
            username: ""
        }
    };

    // Example "from" may not exist at all in the result object.
    // Maybe "from" does exist in result and provides only an "id",
    // but I don't want to overwrite the "id" and still provide
    // the "username" with a default value if there isn't one.
}

I thought about multiple if conditioning hasOwnProperty but I'm wondering is there a better way than a table of if conditions like Object.assign()?

I don't want to require another script or use npm for this.

Answer 1

I've been going through my code snippets and trying to build the functionality I wanted. I've managed to succeed after many hours.

Return a new target object without harming the original.

function defaultsDeep(target, defaults) {
    var clone = JSON.parse(JSON.stringify(target));
    function run(clone, defaults) {
        const DEFAULTS_PROPERTY_NAMES = Object.getOwnPropertyNames(defaults);
        DEFAULTS_PROPERTY_NAMES.forEach(function (property) {
            if (Object.prototype.toString.call(defaults[property]) === "[object Object]") {
                if (!clone.hasOwnProperty(property)) {
                    clone[property] = {};
                }
                run(clone[property], defaults[property]);
            } else if (!clone.hasOwnProperty(property)) {
                clone[property] = defaults[property];
            }
        });
    }
    run(clone, defaults);
    return clone;
}

Example

var result = {
    "message_id": 1,
    "from": {
        "id": 12345
    }
};

const defaults = {
    "from": {
        "id": null,
        "username": ""
    }
};

var newObj = defaultsDeep(result, defaults);
console.log("newObj " + JSON.stringify(newObj));
/* result
{
    "message_id": 1,
    "from": {
        "id": 12345,
        "username": ""
    }
}
*/

I don't know if there's a better way of coding this. But if there is, feel free to edit. Also, if you're wondering why I didn't use for in loop method. It's because jslint discourages it now in es6 and I don't think I can disable the warning.