javascript changes image position

With the widespread application of the Internet and mobile devices, the needs of web design are becoming more and more diverse, and interactivity and dynamic response have become important directions in web design. It is often necessary to use dynamic effects in web pages to increase page interest. Among them, changing the position of the picture is a common effect. This article will introduce how to use JavaScript to achieve the effect of changing the position of the image.

1. Understanding JavaScript

JavaScript is a scripting language used to add interactive effects to web pages. Using JavaScript, you can dynamically change the style, attributes, and content of HTML elements in a web page without reloading the entire page. Since JavaScript can easily operate HTML and CSS, using JavaScript in web design can achieve fine details and increase the user's interactive experience.

2. Change the position of the image

Changing the position of the image is a very basic function in JavaScript. On the page, we often need to dynamically change the position of pictures to achieve special visual effects.

The following is a piece of code that uses JavaScript to change the position of the image:

<style>
#myImg {
  position: absolute;
  left: 0px;
  top: 0px;
}
</style>



<h2 id="JavaScript改变图片位置">JavaScript改变图片位置</h2>

<img  src="/static/imghwm/default1.png" data-src="img.jpg" class="lazy" id="myImg"    style="max-width:90%"  style="max-width:90%" alt="javascript changes image position" >

<p>Klicken Sie auf die Schaltfläche, um das Bild nach rechts zu bewegen:</p>

<button onclick="moveRight()">Rechts bewegen</button>

<script>
function moveRight() {
  var img = document.getElementById("myImg");
  var xpos = img.offsetLeft;
  img.style.left = xpos + 10 + "px";
}
</script>

In the above code, we use the position attribute of CSS to control the position of the image, and the offsetLeft attribute of JavaScript obtains the distance between the image and the parent The distance between the level element (i.e. the left side of the page) and its left value is changed through style.left, thereby realizing the position change of the picture.

3. More ways to change the position of the picture

1. Change the zoom ratio of the picture

In addition to changing the position of the picture, you can also change the picture using JavaScript The scaling ratio makes the image larger or smaller. The following is an example of changing the image scaling:

<style>
#myImg {
  width: 100px;
  height: 100px;
  transition: all 0.5s ease;
}
</style>



<h2 id="JavaScript改变图片缩放比例">JavaScript改变图片缩放比例</h2>

<img  src="/static/imghwm/default1.png" data-src="img.jpg" class="lazy" id="myImg" alt="javascript changes image position" >

<p>Klicken Sie auf das Bild, um es zu vergrößern:</p>

<script>
document.getElementById("myImg").onclick = function() {myFunction()};

function myFunction() {
  var img=document.getElementById("myImg");
  if (img.style.width==="100px"){
    img.style.width="200px";
    img.style.height="200px";
  } else {
    img.style.width="100px";
    img.style.height="100px";
  } 
}
</script>

In the above code, we achieve image scaling by changing the width and height attributes of the image, and at the same time use the transition attribute in CSS to make the image change smoother.

2. Picture dragging effect

In addition to changing the position and scaling of the picture, we can also achieve the dragging effect of the picture through JavaScript. On the web page, we can move the position of the image by dragging it with the mouse.

The following is a code that implements the drag-and-drop effect of an image:

<style>
#myImg {
  position: absolute;
  left: 0px;
  top: 0px;
}
</style>



<h2 id="JavaScript实现图片拖拽效果">JavaScript实现图片拖拽效果</h2>

<img  src="/static/imghwm/default1.png" data-src="img.jpg" class="lazy" id="myImg"    style="max-width:90%"  style="max-width:90%" onmousedown="dragElement(this)" alt="javascript changes image position" >

<script>
function dragElement(elmnt) {
  var pos1 = 0, pos2 = 0, pos3 = 0, pos4 = 0;
  if (document.getElementById(elmnt.id + "header")) {
    document.getElementById(elmnt.id + "header").onmousedown = dragMouseDown;
  } else {
    elmnt.onmousedown = dragMouseDown;
  }

  function dragMouseDown(e) {
    e = e || window.event;
    e.preventDefault();
    pos3 = e.clientX;
    pos4 = e.clientY;
    document.onmouseup = closeDragElement;
    document.onmousemove = elementDrag;
  }

  function elementDrag(e) {
    e = e || window.event;
    e.preventDefault();
    pos1 = pos3 - e.clientX;
    pos2 = pos4 - e.clientY;
    pos3 = e.clientX;
    pos4 = e.clientY;
    elmnt.style.top = (elmnt.offsetTop - pos2) + "px";
    elmnt.style.left = (elmnt.offsetLeft - pos1) + "px";
  }

  function closeDragElement() {
    document.onmouseup = null;
    document.onmousemove = null;
  }
}
</script>

In the above code, we use the mousedown, mousemove, and mouseup events to achieve the drag-and-drop effect. Among them, the mousedown event triggers the element The elementDrag function modifies the left and top attributes of the element during the movement of the element, and the mouseup event ends the dragging process.

4. Summary

The above are some common methods of using JavaScript to change the position of images. By understanding these methods, we can use JavaScript more flexibly to achieve dynamic effects in web design. At the same time, when using JavaScript, you must pay attention to compatibility and performance issues to ensure that web pages can run correctly on different browsers and devices.

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