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How to implement sliding carousel images in js?

零下一度
零下一度Original
2017-07-09 09:40:451503browse

This article mainly introduces in detail the js implementation of the left-to-right sliding carousel effect. It has a certain reference value. Interested friends can refer to the

carousel chart. Let the pictures slide automatically every few seconds to achieve the effect of pictures playing in turn. In terms of effects, carousels can be either sliding or gradual. The sliding carousel is the effect of pictures sliding in from left to right. The gradual carousel is the effect of pictures gradually being displayed based on transparency. What I’m talking about here is the method to achieve the first effect.

Principle

Pictures of the same size are combined into a column, but only one of the pictures is displayed, and the rest are hidden. Change the display by modifying the left value picture.

Click to view the effect

html part

nav is the total container, No. One ul list #index is a list of small dots. Whichever dot is covered by the mouse will display the picture. on is a class that adds a background color attribute to the small dots; the second ul list #img is a list of pictures. 


  <!DOCTYPE html>
  <html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Carousel Figure</title>
    <link rel="stylesheet" href="style.css" rel="external nofollow" >
  </head>
  <body>
  <!--从左向右滑动-->
    <nav>
      <ul id="index">
        <li class="on"></li>
        <li></li>
        <li></li>
        <li></li>
        <li></li>
      </ul>
      <ul id="img">
        <li><img src="../images/img1.jpg" alt="img1"></li>
        <li><img src="../images/img2.jpg" alt="img2"></li>
        <li><img src="../images/img3.jpg" alt="img3"></li>
        <li><img src="../images/img4.jpg" alt="img4"></li>
        <li><img src="../images/img5.jpg" alt="img5"></li>
      </ul>
    </nav>
  <script src="script.js"></script>
  </body>
  </html>

css part

The image sizes are all 720*405, you need to pay attention to the following points here:

ul#The img list is absolutely positioned relative to nav. The length of #img must be set to the total width of all images so that the images can be displayed side by side;

The width of the total container nav must be set to the width of the picture 720px, that is, only one picture can be displayed, and the part beyond the width is hidden, that is, overflow: hidden;

The small dot list should be displayed above the picture list, so Set the z-index of #img: -1;

The small dot list is composed of a series of li by changing the border style, so you only need to change the background color to achieve the effect of moving the small dots. 


  *{
    margin:0;
    padding:0;
  }
  nav{
    width: 720px;
    height: 405px;
    margin:20px auto;
    overflow: hidden;
    position: relative;
  }
  #index{
    position: absolute;
    left:320px;
    bottom: 20px;
  
  }
  #index li{
    width:8px;
    height: 8px;
    border: solid 1px gray;
    border-radius: 100%;
    background-color: #eee;
    display: inline-block;
  }
  #img{
    width: 3600px;/*不给宽高无法移动*/
    height: 405px;
    position: absolute;/*不定义absolute，js无法设置left和top*/
    z-index: -1;
  }
  #img li{
    width: 720px;
    height: 405px;
    float: left;
  }
  #index .on{
    background-color: black;
  }

JS part

Image moving function moveElement()

The moveElement function needs to obtain the current position and target position of the picture and calculate the gap between them to move. You can use offsetLeft and offsetTop to obtain the current position of the picture. The effect of "swiping across" the picture when moving is to divide the distance into 10 times for movement, that is, using the setTimeOut function. However, in order to prevent the mouse from hovering, the clearTimeout() function needs to be called. The code is as follows: 


  function moveElement(ele,x_final,y_final,interval){//ele为元素对象
    var x_pos=ele.offsetLeft;
    var y_pos=ele.offsetTop;
    var dist=0;
    if(ele.movement){//防止悬停
      clearTimeout(ele.movement);
    }
    if(x_pos==x_final&&y_pos==y_final){//先判断是否需要移动
      return;
    }
    dist=Math.ceil(Math.abs(x_final-x_pos)/10);//分10次移动完成
    x_pos = x_pos<x_final ? x_pos+dist : x_pos-dist;
    
    dist=Math.ceil(Math.abs(y_final-y_pos)/10);//分10次移动完成
    y_pos = y_pos<y_final ? y_pos+dist : y_pos-dist;
    
    ele.style.left=x_pos+&#39;px&#39;;
    ele.style.top=y_pos+&#39;px&#39;;
    
    ele.movement=setTimeout(function(){//分10次移动，自调用10次
      moveElement(ele,x_final,y_final,interval);
    },interval)
  }

Small dot moving function moveIndex()

The essence of moving small dots is to move the background color class set on, the principle is to first determine which li has a background color, remove it if there is one, so that all li have no background, and then add a background to the current li. 


  function moveIndex(list,num){//移动小圆点
    for(var i=0;i<list.length;i++){
      if(list[i].className==&#39;on&#39;){//清除li的背景样式
        list[i].className=&#39;&#39;;
      }
    }
    list[num].className=&#39;on&#39;;
  }

Automatic picture rotation

Write the following code directly in window.onload Just hit it.
Here you need to define a variable index, which means moving to the index (0~n-1, n is the number of li) picture. 


  var img=document.getElementById(&#39;img&#39;);
  var list=document.getElementById(&#39;index&#39;).getElementsByTagName(&#39;li&#39;);
  var index=0;//这里定义index是变量，不是属性

  var nextMove=function(){//一直向右移动，最后一个之后返回
    index+=1;
    if(index>=list.length){
      index=0;
    }
    moveIndex(list,index);
    moveElement(img,-720*index,0,20);
  };

The automatic carousel of pictures requires the use of the setInterval() function, which allows the program to automatically call the nextMove() function every few seconds: 


  var play=function(){
    timer=setInterval(function(){
      nextMove();
    },2500);
  };

The effect of mouse covering small dots

If you want to realize which small dot the mouse covers, the corresponding picture will be displayed For this effect, you need to know which small dot is covered by the mouse. Here, add a custom attribute index to each li so that the value of this attribute is the serial number of the corresponding small dot i (0~n-1, n is the number of li), so that every time the mouse covers it, you only need to get the value of the index attribute to know which small dot the mouse covers. Note that the index attribute has nothing to do with the variable index, they only have the same name. 


  for(var i=0;i<list.length;i++){//鼠标覆盖上哪个小圆圈，图片就移动到哪个小圆圈，并停止
    list[i].index=i;//这里是设置index属性，和index变量没有任何联系
    list[i].onmouseover= function () {
      var clickIndex=parseInt(this.index);
      moveElement(img,-720*clickIndex,0,20);
      index=clickIndex;
      moveIndex(list,index);
      clearInterval(timer);
    };
    list[i].onmouseout= function () {//移开后继续轮播
      play();
    };
  }

Summary

The movement behavior of the dots is separated, which makes it easier to implement. This carousel picture actually has some problems. When sliding from the last picture to the first picture, the sliding distance is long. In fact, it is easy to solve. Change the sliding method. Here, the final calculation is based on -720*index. The left value, and index is to tie the movement of the picture and the movement of the small dots together. Change the sliding method to the current offsetLeft+ (-720). The movement of the picture can be independent of the index value, and then add a value to the html file. Pictures: 


<li><img src="../images/img1.jpg" alt="img1"></li>
<li><img src="../images/img2.jpg" alt="img2"></li>
<li><img src="../images/img3.jpg" alt="img3"></li>
<li><img src="../images/img4.jpg" alt="img4"></li>
<li><img src="../images/img5.jpg" alt="img5"></li>
<li><img src="../images/img1.jpg" alt="img1"></li>

Then when sliding to the last picture, quickly assign the offset to 0 and change it to the first picture. The two pictures are the same and cannot be Distinguish the changes and achieve seamless connection. 


  if(x_pos==-3600){
    ele.style.left=&#39;0&#39;;
    ele.style.top=&#39;0&#39;;
  }else{
    ele.style.left=x_pos+&#39;px&#39;;
    ele.style.top=y_pos+&#39;px&#39;;
  }

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