lamb是一组函数.

const sign = ['red', 'green', 'yellow'];

function tic(str, timer) {
  return () => new Promise((res, rej) => {
    setTimeout(() => {
      console.log(str);
      res();
    }, timer);
  });
}

const lamb = sign.reduce(function (prev, item) {
  prev.push(tic(item, 1000));

  return prev;
}, []);

const gen = function* () {
  lamb.forEach(function (item, index) {
    yield item();
  });

  // for(let i = 0; i < lamb.length; i++) {
  //   yield lamb[i]();
  // }

  //for(let i in lamb) {
    //yield lamb[i]();
//  }
}

为什么 forEach不行(报错Unexpected identifier)，for(let i = 0; i < lamb.length; i++) /for(let i in lamb)可以？