小结练习

1.处理时间

<p id="app">10:10:10 </p>
<script>
  function handleTime(value){
    if(value<10){
      return "0"+value
    }else{
      return ""+value
    }
  }
  function showTime(){
    var app = document.getElementById("app")
    var endTime = "2020-12-01 16:50:00"
    /* 1.获取结束时间的毫秒 */
    endTime = new Date(endTime).getTime()
    /* 2.获取当前时间的毫秒 */
    var nowTime = new Date().getTime()
    /* 3.获取他们之间的差  */
    var gapTime = endTime-nowTime
    /* 4.将他们的差转化为时分秒 */
    var seconds = Math.floor(gapTime/1000);
    var hours = handleTime(Math.floor(seconds/3600));
    seconds = seconds%3600;
    var minutes = handleTime(Math.floor(seconds/60));
    seconds = handleTime(seconds%60);//不需要向下取整
    var sum = hours+":"+minutes+":"+seconds;
    app.innerHTML = sum
    /* 超时调用
      setTimeout(fucntion(){
        showTime()
      },1000)
    */
  }
  showTime();
  /* 间歇调用 */
  setInterval(function(){
    showTime()
  },1000)
</script>

2.动态时钟

<div id="box">
  <img src="images/0.png" alt="">
  <img src="images/0.png" alt="">
  <span class="colon">:</span>
  <img src="images/0.png" alt="">
  <img src="images/0.png" alt="">
  <span class="colon">:</span>
  <img src="images/0.png" alt="">
  <img src="images/0.png" alt="">
</div>

function handleTime(value){
  if(value<10){
    return "0"+value
  }else{
    return ""+value
  }
}
function showTime(){
  var imgs = document.querySelectorAll("#box img")
  var d = new Date()
  var hours = handleTime(d.getHours())
  var minutes = handleTime(d.getMinutes())
  var seconds = handleTime(d.getSeconds())
  var sum = hours+minutes+seconds;
  // console.log(sum);
  // console.log(typeof sum);
  for(var i=0;i<imgs.length;i++){
    //imgs[i].src = "images/"+sum[i]+".png"
    // 字符串模板：可以在字符串中使用变量 ${}
    imgs[i].src = `images/${sum[i]}.png`
  }
  setTimeout(function(){//最好写超时调用
    showTime()
  },1000)
}
showTime()