实现lazyMan

涉及的知识点：

1. 流程控制：创建task任务队列，使用push、shift、unshift方法操作任务
2. 闭包：当闭包中的值引用自闭包外部，那么这些值会始终存放在内存中。下面例子中的name、time都会保存在内存中，不至于访问时为undefined

      function _lazyMan (name) {

        // 创建一个任务队列
        this.task = [];
        let self = this;

        let fn = (function (name) {
          return function () {
            console.log(`Hi! This is ${name}!`);
            // 执行下一个任务
            self.next();
          };
        })(name);
        this.task.push(fn);
        // 在下一个事件循环启动任务
        setTimeout(function () {
          self.next();
        }, 0);
      }

      _lazyMan.prototype.next = function () {
        let fn = this.task.shift();
        fn && fn();
      };

      _lazyMan.prototype.sleepFirst = function (time) {
        let self = this;
        let fn = (function (time) {
          return function () {
            setTimeout(function () {
              console.log(`Wake up after ${time}s!`);
              self.next();
            }, time * 1000);
          }
        })(time);
        this.task.unshift(fn);
        return this;
      }

      _lazyMan.prototype.sleep = function (time) {
        let self = this;
        let fn = (function (time) {
          return function () {
            setTimeout(function () {
              console.log(`Wake up after ${time}s!`);
              self.next();
            }, time * 1000);
          }
        })(time);
        this.task.push(fn);
        return this;
      }

      _lazyMan.prototype.eat = function (name) {
        let self = this;
        let fn = (function (name) {
          return function () {
            console.log(`Eat ${name}~`)
            self.next();
          }
        })(name);
        this.task.push(fn);
      }

      function lazyMan (name) {
        return new _lazyMan(name);
      }

      lazyMan('17khba').sleepFirst(10).eat('lunch');