红路灯

红路灯

题目: 红灯三秒亮一次，绿灯一秒亮一次，黄灯2秒亮一次；如何让三个灯不断交替重复亮灯？（用Promse实现）

function red() {
 console.log('red');
}

function green() {
 console.log('green')
}

function yellow() {
 console.log('yellow')
}

function light(timer, cb) {
 return new Promise((resolve) => {
  setTimeout(() =>{
   cb();
   resolve();
  }, timer);
 });
}

function step() {
 [() => light(3000, red), () => light(2000, green), () => light(1000, yellow)].reduce((acc, cur) => {
  return acc.then(cur);
 }, Promise.resolve())
 .then(() => step());
}

step();