JavaScript implements image mobile terminal-Front-end Q&A-php.cn

In modern mobile applications, the use of images is widespread and common, so it is very necessary for developers to master the method of using JavaScript to implement images on the mobile terminal. Below we will introduce how to use JavaScript to implement images on the mobile terminal.

First of all, to move the image, we need to define a container in which the image element will be nested. We can use HTML tag elements to complete the creation of this container. For simpler application scenarios, the

element can be used as a container. For example:

<div id="container">
   <img src="img/mypic.jpg" alt="My Picture">
</div>

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In the Document Object Model (DOM), JavaScript uses document.getElementById() to get HTML elements. We can set the id attribute of

to "container" and use document.getElementById() to obtain its reference. After that, we also need to get a reference to the image element.

var container = document.getElementById('container');
var img = container.getElementsByTagName('img')[0];

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With the increasing popularity of touch devices, developers need to pay more attention to the interactivity of the interface for mobile applications. In this case, it is very important to monitor finger sliding events. We can use JavaScript to write the following code to achieve this:

var xStart, yStart, xMove, yMove, xEnd, yEnd;

img.addEventListener('touchstart', function(e){
   xStart = e.touches[0].pageX;
   yStart = e.touches[0].pageY;
});

img.addEventListener('touchmove', function(e){
   xMove = e.touches[0].pageX;
   yMove = e.touches[0].pageY;

   var xOffset = xMove - xStart;
   var yOffset = yMove - yStart;

   img.style.transform = 'translateX(' + xOffset + 'px) 
                                     translateY(' + yOffset + 'px)';
});

img.addEventListener('touchend', function(e){
   xEnd = e.changedTouches[0].pageX;
   yEnd = e.changedTouches[0].pageY;

   var xOffset = xEnd - xStart;
   var yOffset = yEnd - yStart;

   img.style.transform = 'translateX(' + xOffset + 'px) 
                                     translateY(' + yOffset + 'px)';
});

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In the above code, we are using touch events. When the user slides the picture, we will listen for a touchmove event. At this point, we can get the distance the user's finger moved and update the position of the picture based on this distance.

Among them, touch events include three types: touchstart, touchmove and touchend. touchstart means the finger starts touching the screen, touchmove means the finger moves on the screen, and touchend means the finger leaves the screen. For each type of event, we will define corresponding logic to realize the movement of the picture.

Finally, we need to pay attention to another issue. For mobile devices, users' touch operations are often diverse and complex. Therefore, event processing can be optimized according to special needs. For incompatible browsers, we should use alternative solutions to solve cross-browser issues.

In actual applications, we need to consider the location, size, loading time and other factors of the image, and perform corresponding application optimization according to needs. JavaScript can help us achieve these effects. When using JavaScript, we need to pay attention to performance issues and exercise appropriate control over these factors.

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source：php.cn

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