Use javascript to change pictures regularly

JavaScript is a commonly used scripting language that can be used on various web pages to achieve very rich functions. Among them, regularly modifying pictures is a common application, which can make web pages more lively and interesting, and also has certain practical value. This article will explore how to use JavaScript to change images regularly and the implementation details.

1. JavaScript timer

Before introducing how to use JavaScript to regularly modify images, it is necessary to first understand the JavaScript timer. JavaScript timer is a function used to perform scheduled tasks. It can be used to implement functions such as regularly modifying pictures and regularly refreshing pages.

JavaScript provides two timers:

1. setInterval(): implements the function of repeatedly executing a function or statement.
2. setTimeout(): implements the function of executing a function or statement after a delay.

In this article, we will use setInterval() to implement the function of regularly modifying pictures.

2. Modify pictures regularly

We can implement the function of modifying pictures regularly using JavaScript through the following steps:

1. Prepare the pictures that need to be rotated, and Define a variable to record the serial number of the currently displayed picture.

For example, we assume that there are 3 pictures on the page, their file names are "img1.jpg", "img2.jpg" and "img3.jpg", and we define a variable currentIndex To record the serial number of the currently displayed picture.

var currentIndex = 1;

2. Write a function to modify the displayed image and update the value of currentIndex.

For example, we define a function named changeImage to switch pictures and update the value of currentIndex. The method of switching pictures can be determined according to actual needs.

function changeImage(){

var imgElement = document.getElementById("img");
switch(currentIndex){
    case 1:
        imgElement.src = "img2.jpg";
        currentIndex = 2;
        break;
    case 2:
        imgElement.src = "img3.jpg";
        currentIndex = 3;
        break;
    case 3:
        imgElement.src = "img1.jpg";
        currentIndex = 1;
        break;
}

}

3. Use the setInterval function to execute the changeImage function regularly.

For example, we define a variable named timer to store the ID value returned by the setInterval function, and define a variable named duration to set the timing period. After the page is loaded, we call the setInterval function to execute the changeImage function and pass in the period parameter duration.

var timer;
var duration = 3000; // 3 seconds
window.onload = function(){

timer = setInterval(changeImage, duration);

}

4. Place a picture element on the page and set an ID value for it.

For example, we place an img element on the page and set an ID value to "img". Note that the ID value must be unique and cannot conflict with the ID values ​​of other elements on the page.

In this way, we have successfully used JavaScript timer to implement the image carousel function.

3. Optimization Suggestions

In order to make the image carousel effect more natural and smooth, we can optimize for different actual situations, such as:

1. Preload images : After the page is loaded, preload all images that need to be rotated, which can reduce delays and freezes when switching images.
2. Use CSS animation: Through the transition and transform properties of CSS3, you can achieve smoother animation effects and improve user experience.
3. Consider mobile adaptation: On mobile browsers, there may be problems with the effect of the image carousel, and corresponding adaptation and adjustments are required.

4. Summary

Through the introduction of this article, we learned how to use JavaScript timer to implement the image carousel function. The implementation process is not complicated, and you only need to master basic JavaScript syntax and how to use timers. Of course, in order to achieve better results, we still need to make some optimizations and improvements. I hope readers and classmates can gain a deeper understanding in practice and create better carousel effects.

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