微信笔试题：LazyMan实现

实现一个函数LazyMan，执行情况如下：

LazyMan("Hank")
// 输出:Hi! This is Hank!
 
LazyMan("Hank").sleep(10).eat("dinner")
// 输出 Hi! This is Hank!
// 等待10秒..
// 输出 Wake up after 10
// 输出 Eat dinner
 
LazyMan("Hank").eat("dinner").eat("supper")
// 输出 Hi This is Hank!
// 输出 Eat dinner
// 输出 Eat supper
 
LazyMan("Hank").sleepFirst(5).eat("supper")
// 等待5秒
// 输出 Hi This is Hank!
// 输出 Eat supper

在有Promise的情况下，还是很好做的：

function LazyMan(name) {
  function sleep(time) {
    return new Promise(resolve => setTimeout(resolve, time * 1000));
  }

  function addToQueue(queue, item, addToHead) {
    queue[addToHead ? 'unshift' : 'push'](item);
  }

  function resolvePromiseQueue(queue) {
    queue.reduce((last, cur) => {
      return last.then(cur);
    }, Promise.resolve());
  }

  const QUEUE_NAME = Symbol('QueueName'); // 通过Symbol ,使queue成为“私有”成员

  return new class LazyMan {
    constructor() {
      this[QUEUE_NAME] = [() => console.log(`Hi! This is ${name}!`)];
      Promise.resolve().then(resolvePromiseQueue.bind(null, this[QUEUE_NAME]));
    }
    eat(food) {
      addToQueue(this[QUEUE_NAME], () => console.log(`Eat ${food}`));
      return this;
    }
    sleep(time, sleepFirst) {
      addToQueue(
        this[QUEUE_NAME],
        () => sleep(time).then(() => console.log(`Wake up after ${time}`)),
        sleepFirst
      );
      return this;
    }
    sleepFirst(time) {
      this.sleep(time, true);
      return this;
    }
  }();
}