deep-equal.mjs

const person1 = {
    "firstName": "John",
    "lastName": "Doe",
    "age": 35
};

const person2 = {
    "firstName": "John",
    "lastName": "Doe",
    "age": 35,
};

const isDeepEqual = (object1, object2) => {

    const objKeys1 = Object.keys(object1);
    const objKeys2 = Object.keys(object2);

    if (objKeys1.length !== objKeys2.length) return false;

    for (var key of objKeys1) {
        const value1 = object1[key];
        const value2 = object2[key];

        const isObjects = isObject(value1) && isObject(value2);

        if ((isObjects && !isDeepEqual(value1, value2)) ||
            (!isObjects && value1 !== value2)
        ) {
            return false;
        }
    }
    return true;
};

const isObject = (object) => {
    return object != null && typeof object === "object";
};

console.log(isDeepEqual(person1, person2)); //true