text: class C1 {
    constructor(countdown) {
      if (countdown > 0) {
        this.c2 = new C2(countdown - 1)
      }
      else {
        this.c2 = 0;
      }
      console.log('c1');
    }
  }
  
  class C2 {
    constructor(countdown) {
      this.countdown = countdown;
      this.c1 = new C1(countdown - 1);
      console.log('c2');
    }
  }
  
  let c = new C1(10);