const config = {
  host: "localhost",
  port: 3000,
  db: {
    name: "mydb",
    maxConnections: 10
  }
};

Object.freeze(config);

config.port = 9999;
config.db.maxConnections = 99;
config.newProp = "surprise";
delete config.host;

const sealed = Object.seal({ x: 1, y: 2 });
sealed.x = 100;
sealed.z = 999;
delete sealed.y;

console.log(config.port, config.db.maxConnections, config.host);
console.log(sealed.x, sealed.y, sealed.z);