Five easy steps to implement JavaScript HTML clock effect

This article mainly introduces the five-step code to easily implement JavaScript HTML clock effect. It has certain reference and value for learning JavaScript. Friends who are interested in JavaScript can refer to it. This article

After learning HTML, CSS and JS for a period of time, I will make a beautiful and not powerful HTML clock for everyone. First look at the picture:

The knowledge points involved are: CSS3 animation, DOM operation, timer, calculation of dot coordinates (many people have already returned it to their teachers~)
Next, we use 5 steps To make it

step1,Prepare HTML

First, we need to prepare the HTML structure, background, dial, hands (hour hand, minute hand, second hand), and numbers.

<p id="clock">
 <p class="bg">
  <p class="point">
   <p id="hour"></p>
   <p id="minute"></p>
   <p id="second"></p>
   <p class="circle"></p>
  </p>
 </p>
< /p>

step2, Prepare CSS

Define the color and size of the pointer. What needs to be explained is transform: rotate(-90deg); used to rotate the pointer, transform- origin:0 6px; is used to set the rotation center point.

<style>
 *{
  margin: 0;
  padding: 0;
 }
 #clock{
  margin: 5% auto;
  width: 400px;
  height: 400px;
  border-radius: 10px;
  background: #aaa;
  position: relative;
  transform: rotate(-90deg);
 }
 #clock .bg{
  width: 360px;
  height: 360px;
  border-radius: 50%;
  background: #fff;
  position: absolute;
  left: 50%;
  top: 50%;
  margin-left: -180px;
  margin-top: -180px;
 }
 #clock .point{
  position: absolute;
  left: 50%;
  top: 50%;
  margin-left: -14px;
  margin-top: -14px;
 }
 #clock #hour{
  width: 80px;
  height: 16px;
  background: #000;
  margin: 6px 0 0 14px;
  /*transform: rotate(30deg);*/
  transform-origin:0 8px;
  /*animation: hour 3s linear 100!* alternate*!;*/
  border-radius: 16px;
 }

 #clock #minute{
  width: 120px;
  height: 12px;
  background: #000;
  margin: -14px 0 0 14px;
  transform-origin:0 6px;
  border-radius: 12px;
 }
 #clock #second{
  width: 160px;
  height: 6px;
  background: #f00;
  margin: -9px 0 0 14px;
  transform-origin:0 3px;
  border-radius: 6px;
 }
 #clock .point .circle{
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: #000;
  position: absolute;
  left: 0;
  top: 0;
 }
 @keyframes hour {
  from {transform: rotate(0deg);}
  to {transform: rotate(360deg);}
 }

 #clock .number{
  position: absolute;
  font-size: 34px;
  width: 50px;
  height: 50px;
  line-height: 50px;
  text-align: center;
  transform: rotate(90deg);
 }
< /style>

step3, Calculate the hour hand position

JS obtains the current time through the Date object, getHours obtains the hour, getMinutes obtains the minute, and getSeconds obtains the second. One rotation of the hour hand is 12 divisions, and the angle of each division is 360°/12. The minutes and seconds are both 60 divisions, and the angle of each division is 360°/60.

function clock(){
 var date = new Date();//获取当前时间
 //时(0-23) 分(0-59)秒(0-59)
 //计算转动角度
 var hourDeg = date.getHours()*360/12;
 var minuteDeg = date.getMinutes()*360/60;
 var secondDeg = date.getSeconds()*360/60;
 //console.log(hourDeg, minuteDeg, secondDeg);
 //设置指针
 hour.style.transform = 'rotate('+hourDeg+'deg)';
 minute.style.transform = 'rotate('+minuteDeg+'deg)';
 second.style.transform = 'rotate('+secondDeg+'deg)';
}

step4, Clock rotation

Set the timer through setInterval and refresh it every second. Note that the initialization needs to be executed once, otherwise the effect will not be visible until 1s later.

//初始化执行一次
clock();
setInterval(clock,1000);

step5, Drawing digital time

Digital time is also on a circle. We only need to determine the radius, and then get the coordinates on the radius. Just position each number by the left side. Take a look at the calculation rules of the circular coordinate system:

* Calculation of circular radius coordinates:
* x = pointX + r*cos(angle);
* y = pointY + r*sin(angle);
But note that the coordinates we calculate are the coordinates of the point on the arc. When positioning each number, it is positioned based on the upper left corner point of the element, so that our numbers There will be an offset. That is to say, the center point of the number is not on the arc. The solution is to translate the coordinate point (x, y) by half of itself (x-w/2, y-h/2)
, so that the center point of the number is on the arc. .

var pointX = 200;
var pointY = 200;
var r = 150;
function drawNumber(){
 var deg = Math.PI*2/12;//360°
 for (var i = 1; i <= 12; i++) {
  //计算每格的角度
  var angle = deg*i;
  //计算圆上的坐标
  var x = pointX + r*Math.cos(angle);
  var y = pointY + r*Math.sin(angle);
  //创建p,写入数字
  var number = document.createElement(&#39;p&#39;);
  number.className = &#39;number&#39;;
  number.innerHTML = i;
  //减去自身的一半, 让p的中心点在圆弧上
  number.style.left = x - 25 + &#39;px&#39;;
  number.style.top = y - 25 + &#39;px&#39;;
  //添加到页面
  myClock.appendChild(number);
 }
}

Complete JS code:

<script>
 /***
  * 时钟:
  * 1> 旋转: rotate(90deg)
  * 2> 旋转中心点: transform-origin
  * */
 //TODO step1: 获取时钟的指针
 var hour = document.getElementById(&#39;hour&#39;);//时针
 var minute = document.getElementById(&#39;minute&#39;);//分针
 var second = document.getElementById(&#39;second&#39;);//秒针
 var myClock = document.getElementById(&#39;clock&#39;);//时钟

 //TODO step2: 获取当前时间,把指针放在正确的位置
 function clock(){
  var date = new Date();//获取当前时间
  //时(0-23) 分(0-59)秒(0-59)
  //计算转动角度
  var hourDeg = date.getHours()*360/12;
  var minuteDeg = date.getMinutes()*360/60;
  var secondDeg = date.getSeconds()*360/60;
  //console.log(hourDeg, minuteDeg, secondDeg);
  //设置指针
  hour.style.transform = &#39;rotate(&#39;+hourDeg+&#39;deg)&#39;;
  minute.style.transform = &#39;rotate(&#39;+minuteDeg+&#39;deg)&#39;;
  second.style.transform = &#39;rotate(&#39;+secondDeg+&#39;deg)&#39;;
 }
 //初始化执行一次
 clock();
 //TODO step3: 设置定时器
 setInterval(clock,1000);

 /***
  * 圆半径坐标计算：
  * x = pointX + r*cos(angle);
  * y = pointY + r*sin(angle);
  * */
 var pointX = 200;
 var pointY = 200;
 var r = 150;
 //TODO step4: 画时钟数字
 function drawNumber(){
  var deg = Math.PI*2/12;//360°
  for (var i = 1; i <= 12; i++) {
   //计算每格的角度
   var angle = deg*i;
   //计算圆上的坐标
   var x = pointX + r*Math.cos(angle);
   var y = pointY + r*Math.sin(angle);
   //创建p,写入数字
   var number = document.createElement(&#39;p&#39;);
   number.className = &#39;number&#39;;
   number.innerHTML = i;
   //减去自身的一半, 让p的中心点在圆弧上
   number.style.left = x - 25 + &#39;px&#39;;
   number.style.top = y - 25 + &#39;px&#39;;
   //添加到页面
   myClock.appendChild(number);
  }
 }
 drawNumber();
< /script>

The above is the entire content of this article, I hope it will be helpful to everyone’s learning! !

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