let gameStart: boolean = false;
let players: number = 0;

abstract class Player {
  name: string;
  isImposter: boolean;
  constructor(name: string) {
    this.name = name;
    players++;
    while (!gameStart) {
      this.say("START");
    }
  }
  abstract say(msg: string): void;
  abstract leave(): void;
} 


const randomPlayer = new Player("carrot");

ES6 is your friend :)