async await 实现红绿灯

async function dolight(){
	while (true) { // 用于循环 不加只执行一次
      await changeColor(3000,'green')
      await changeColor(1000,'yellow')
      await changeColor(2000,'red')
    }    
}

async function changeColor(duration,color){
  document.getElementById("light").style.background = color;
  await sleep(duration)
},

function sleep(duration){
	return new Promise((resolve)=>{
      setTimeout(resolve,duration)
    })
}

dolight()