async await ​

/* 自动执行next */
  function co (gen) {
      return new Promise((res, rej) => {
        let next = (params) => {
          try {
            /* 获取yield右边表达式 */
            var {value, done} = gen.next(params)
          } catch (e) {
            return rej(e)
          }
          /* 根据done判断是否结束 */
          if (done) {
            res(value)
          } else {
            /* 用promise包裹，兼容value的值为promise */
            Promise.resolve(value).then(data => {
              --data
              /* 递归执行，实现自动 */
              next(data)
            })
          }
        }
        /* 开启执行 */
        next()
      })
    }

    function promiseCreater (params) {
      return new Promise((res, rej) => {
        setTimeout(() => {
          res(params)
        }, 1000)
      })
    }
    
    function* gen(params) {
      let data1 = yield promiseCreater(params)
      console.log(data1)
      let data2 = yield promiseCreater(data1)
      console.log(data2)
      let data3 = yield promiseCreater(data2)
      console.log(data3)
      return data3
    }

    co(gen(100))