js之Promise练习

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红绿黄每隔一秒亮一次；如何让三个灯不断交替重复亮灯？
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function red(){
  console.log('red-   ', new Date());
}
function green(){
  console.log('green-   ', new Date());
}
function yellow(){
  console.log('yellow-   ', new Date());
}

// 地域回调
function fn() {
  setTimeout(() => {
    red()
    setTimeout(() => {
      green()
      setTimeout(() => {
        yellow()
        fn()
      }, 1000)
    }, 1000)
  }, 1000)
}
fn()

// Promise实现
function tic(callback, timer) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      callback()
      resolve()
    }, timer)
  })
}
function fn1 () {
  return tic(red, 1000).then(() => {
    return tic(green, 1000)
  }).then(() => {
    return tic(yellow, 1000)
  }).then(() => {
    fn1()
  })
}
fn1()

// Generator实现
function* light(){
    yield tic(1000, red);
    yield tic(2000, green);
    yield tic(3000, yellow);
}
function loop(iterator, gen){
    var result = iterator.next();
    if (result.done) {
        loop(gen(), gen)
    } else {
        result.value.then(function(){
            loop(iterator, gen)
        })
    }
};
loop(light(), light);

// async, await实现
(async function (){
    while(true){
        await tic(3000, red);
        await tic(2000, green);
        await tic(1000, yellow);
    }
})();