音乐播放器 #

function createPlayer(totalDuration: any) {
  let currentTimer = 0;
  const listener: any[] = [];
  let timer: any = null;
  const nextTimeout = (callback: any) => {
    timer = setTimeout(() => {
      const ret = callback();
      if (ret === false) return;
      nextTimeout(callback);
    }, 1000);
  };

  const playing = () => {
    listener.forEach((fn) => {
      fn(Math.floor((currentTimer * 100) / totalDuration));
    });
    currentTimer = currentTimer + 1000;
    return currentTimer < totalDuration;
  };

  return {
    play() {
      playing() && nextTimeout(playing);
    },
    on(callback: any) {
      listener.push(callback);
    },
    pause() {
      listener.forEach((fn) => {
        fn(Math.floor((currentTimer * 100) / totalDuration));
      });
      clearTimeout(timer);
    },
    stop() {
      currentTimer = 0;
      this.pause();
    },
  };
}

// 使下面的测试代码按要求输出结果
const player = createPlayer(10 * 1000); // 播放 10s 的歌曲
let start = Date.now();
let getTimeSpan = () => Math.floor((Date.now() - start) / 1000);

player.on((progress: any) => {
  console.log(`${getTimeSpan()}s: ${progress}%`);
});

player.play();

setTimeout(() => {
  player.pause();
}, 2000);

setTimeout(() => {
  player.play();
}, 4000);

setTimeout(() => {
  player.stop();
}, 6000);

// output
// 开始后，输出:   0s: 0%
// 1s 后，输出:   1s: 10%
// 2s 后，输出:   2s: 20%
// 3s 后，没有任何输出
// 4s 后，输出:   4s: 20%
// 5s 后，输出:   5s: 30%
// 6s 后，输出:   6s: 0%