JSFiddle - React, Tailwind, and code Playground

JavaScript

function FooManager() {
    this.objects = {};

    this.update = function(data) {
        var self = this;
        $.each(data, function(i, e) {
            var foo = self.objects[i];
            if (typeof foo === "undefined") {
                foo = new Foo(e);
                self.objects[i] = foo;
            } else if (foo instanceof Foo) {
                foo.update(e);
            }
        });
    }
    return this;
}

function Foo(data) {
    this.name = data.name;
    this.age = data.age;
    return this;
}

Foo.prototype.update = function(data) {
    this.name = data.name;
    this.age = data.age;
}

//------ Update 1 --------//

var appData = {
    "0": {
        name: "a",
        age: 2
    },
    "1": {
        name: "b",
        age: 3
    }
}

var fooManager = new FooManager();
fooManager.update(appData);
console.log(fooManager.objects[0]);

//------ Update 2 --------//

var newAppData = {
    "0": {
        name: "a",
        age: 443
    }
}

fooManager.update(newAppData);
console.log(fooManager.objects[0]);