tf-22.ts

function userCount() { 
  /* Mock data */
  return 15;
};

class User {
  id = 0;
  static count: number = 0;

  constructor(
    public username: string,
    public age: number
  ) {
    this.id = ++User.count;
  }

  static {
    User.count += userCount();
  }
}


console.log(User.count); // 15
new User('John', 23);
new User('Suzi', 31);
console.log(User.count); // 17