public class Person
{
    public string FirstName = string.Empty;
    public string LastName = string.Empty;
    public string Age = 0;
    // Other 20 to 30 properties.
}

Person person = new Person()
{
    FirstName = "Nithin",
    LastName = "B",
    Age = 24,
    // Other 20 to 30 properties.
};

Console.WriteLine(person.FirstName);

var Person = function () {
  this.FirstName = "";
  this.LastName = "";
  this.Age = 0;
};

var person = new Person();
person.FirstName = "Nithin";
person.LastName = "B";
person.Age = 24;

console.log(person.FirstName);
console.log(person["FirstName"]);