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Use JavaScript functions to implement image carousels and slideshow effects

王林Original: 2023-11-04 08:59:171570browse

JavaScript is a scripting language that can be used to add interactive effects to web pages. Among them, image carousel and slideshow effects are common web page animation effects. This article will introduce how to use JavaScript functions to achieve these two effects and provide specific code examples.

Picture carousel

Picture carousel is an effect that plays multiple pictures in turn in a certain way. When implementing image carousels, JavaScript timers and CSS style controls need to be used.

(1) Preparation

First, in the HTML file, you need to define a div container to display the carousel image. We can define another ul element to store all the images that need to be rotated. Each li element contains an image.

<div id="slider">
  <ul>
    <li><img  src="img1.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" ></li>
    <li><img  src="img2.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" ></li>
    <li><img  src="img3.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" ></li>
    <li><img  src="img4.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" ></li>
  </ul>
</div>

In the CSS file, some styling needs to be done on these elements. For example, set the width and height of the div container to the actual size of the image, and set the overflow attribute to hidden, so that the portion beyond the container can be hidden. At the same time, set the width of the ul element to the sum of the widths of all images, and set the height to the actual height of the image.

#slider {
  width: 600px;
  height: 400px;
  overflow: hidden;
  position: relative;
}

#slider ul {
  width: 2400px; /* 4张图片的宽度之和 */
  height: 400px;
  position: absolute;
  left: 0;
}

(2) Carousel implementation

Next, we need to use JavaScript functions to achieve the carousel effect. The specific implementation process is as follows:

① Define a variable index to record the serial number of the currently displayed picture.

var index = 0;

② Write a carousel function to switch pictures at certain intervals and update the value of the index variable. In this function, the left value of the ul element needs to be set to the opposite number (negative number) of the width of the current image, so that the carousel effect can be achieved.

function slide() {
  index++;
  if (index >= 4) {  // 图片总数为4，如果index超过4，就将其重置为0
    index = 0;
  }
  var leftVal = -index * 600 + "px";  // 每次切换，将ul元素的left值设置为当前图片的宽度的相反数
  $("#slider ul").stop().animate({left: leftVal}, 500);  // 使用jQuery的animate方法实现滑动效果
}

In the above code, we use the animate() method in the jQuery library, which can be used to achieve animation effects. The animate() method accepts two parameters. The first parameter is an object used to set the CSS properties and values of the animation. Here we set the left attribute of the ul element; the second parameter is a number used to specify the animation run. time, in milliseconds.

③ Call the carousel function and use the setInterval() method to execute it regularly.

setInterval(slide, 2000);

In the above code, we use the setInterval() method, which can be used to execute specified code regularly. The first parameter is the name of the function to be executed regularly, and the second parameter is the time interval in milliseconds.

Finally, the implementation code of the entire picture carousel is as follows:

<!DOCTYPE html>
<html>
<head>
  <title>图片轮播</title>
  <meta charset="utf-8">
  <style>
    #slider {
      width: 600px;
      height: 400px;
      overflow: hidden;
      position: relative;
    }

    #slider ul {
      width: 2400px;
      height: 400px;
      position: absolute;
      left: 0;
    }

    #slider ul li {
      float: left;
    }
  </style>
  <script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
  <script>
    $(function () {
      var index = 0;

      function slide() {
        index++;
        if (index >= 4) {
          index = 0;
        }
        var leftVal = -index * 600 + "px";
        $("#slider ul").stop().animate({left: leftVal}, 500);
      }

      setInterval(slide, 2000);
    })
  </script>
</head>
<body>
  <div id="slider">
    <ul>
      <li><img  src="img1.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" ></li>
      <li><img  src="img2.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" ></li>
      <li><img  src="img3.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" ></li>
      <li><img  src="img4.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" ></li>
    </ul>
  </div>
</body>
</html>

Slideshow effect

The slideshow effect is a way to combine multiple pictures The effect of switching pictures in a certain order. When implementing slide effects, JavaScript event listening and CSS style control are required.

(1) Preparation

Similarly, in the HTML file, a div container needs to be defined to display the slide. We can define multiple img elements, each img element contains a picture.

<div id="slideshow">
  <img  src="img1.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" >
  <img  src="img2.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" >
  <img  src="img3.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" >
  <img  src="img4.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" >
</div>

In the CSS file, we need to style these elements. For example, set the width and height of the div container to the actual size of the image, and set the overflow attribute to hidden; set the position of all img elements to absolute so that they can overlap; and set all but the first image The image's transparency is set to 0.

#slideshow {
  width: 600px;
  height: 400px;
  overflow: hidden;
  position: relative;
}

#slideshow img {
  position: absolute;
  top: 0;
  left: 0;
  opacity: 0;
}

#slideshow img:first-child {
  opacity: 1;
}

In the above code, we use the :first-child pseudo-class to set the transparency of the first image to 1.

(2) Slideshow implementation

Next, we need to use JavaScript functions to achieve the slideshow effect. The specific process is as follows:

① Define a variable index to record the serial number of the currently displayed picture.

var index = 1;

② Write a function to switch pictures and update the value of the index variable. In this function, we first set the transparency of the currently displayed image to 0, then add 1 to the value of the index variable, and determine whether the total number of images is exceeded. If exceeded, reset it to 1. Then set the transparency of the next image to 1 and animate it.

function show() {
  $("#slideshow img:nth-child(" + index + ")").stop().animate({opacity: 0}, 1000); // 当前图片透明度减少
  index++;
  if (index > 4) {
    index = 1;
  }
  $("#slideshow img:nth-child(" + index + ")").stop().animate({opacity: 1}, 1000); // 下一张图片透明度增加
}

In the above code, we use the :nth-child selector, which can select a child element under the specified parent element. In this example, we use this selector to select the index image.

③ Use the setInterval() method to execute the show function regularly.

$(function () {
  setInterval(show, 3000);
})

In the above code, we use the $() method and setInterval() method of the jQuery library to implement scheduled calls. The $() method is used to obtain the specified element, and the setInterval() method can call the specified function periodically.

Finally, the implementation code of the entire slide effect is as follows:

<!DOCTYPE html>
<html>
<head>
  <title>幻灯片效果</title>
  <meta charset="utf-8">
  <style>
    #slideshow {
      width: 600px;
      height: 400px;
      overflow: hidden;
      position: relative;
    }

    #slideshow img {
      position: absolute;
      top: 0;
      left: 0;
      opacity: 0;
    }

    #slideshow img:first-child {
      opacity: 1;
    }
  </style>
  <script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
  <script>
    $(function () {
      var index = 1;

      function show() {
        $("#slideshow img:nth-child(" + index + ")").stop().animate({opacity: 0}, 1000);
        index++;
        if (index > 4) {
          index = 1;
        }
        $("#slideshow img:nth-child(" + index + ")").stop().animate({opacity: 1}, 1000);
      }

      setInterval(show, 3000);
    })
  </script>
</head>
<body>
  <div id="slideshow">
    <img  src="img1.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" >
    <img  src="img2.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" >
    <img  src="img3.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" >
    <img  src="img4.jpg" alt="Use JavaScript functions to implement image carousels and slideshow effects" >
  </div>
</body>
</html>

Through the above code examples, we have implemented the use of JavaScript functions to achieve image carousel and slide effects, and introduced specific implementation process. These technologies are very helpful for improving web page interaction and animation effects. Readers can modify and optimize according to actual needs and continuously improve their development capabilities.

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