class Lazyman {

  constructor() {

    this.tasks = [];

    this.init();

  }

  init() {

    const task = () => {

      console.log('i am a lazyman');

      this.next();

    };

    this.tasks.unshift(task);

    setTimeout(() => {

      this.next();

    }, 0);

  }

  next() {

    if (this.tasks.length) this.tasks.shift()();

  }

  sleep(timer) {

    const task = () => {

      setTimeout(() => {

        console.log(`sleep ${timer}s`);

        this.next();

      }, timer * 1000);

    };

    this.tasks.push(task);

    return this;

  }

  eat(food) {

    const task = () => {

      console.log(`eat ${food}`);

    };

    this.tasks.push(task);

    return this;

  }

}

const aMan = new Lazyman();

aMan

  .sleep(1)

  .eat('orange')

  .sleep(2);