SoFunction
Updated on 2025-04-10

Example of method of using JavaScript to operate Visual Viewport

introduction

In modern front-end development, viewport is a very important concept. It determines what users see when browsing web pages. With the popularity of mobile devices and various screen sizes, it is particularly important to manage the viewport efficiently. JavaScript provides a powerful interface - Visual Viewport API, allowing developers to more flexibly control and obtain viewport information. This article will explain in detail how to use the Visual Viewport API and demonstrate its application with some sample code.

What is the Visual Viewport API

The Visual Viewport API is a set of interfaces that allow developers to obtain detailed information of the viewport and monitor changes in the viewport. This API contains the following important properties:

  • : The width of the viewport.
  • : The height of the viewport.
  • : Current scaling.
  • : The left offset of the upper left corner of the viewport relative to the layout viewport.
  • : The upper offset of the upper left corner of the viewport relative to the layout viewport.

How to use the Visual Viewport API

Using the Visual Viewport API is very simple. First, we need to make sure that the browser supports this API. It can be detected by the following code:

if ('visualViewport' in window) {
    ('Your browser supports Visual Viewport API');
} else {
    ('Your browser does not support the Visual Viewport API');
}

Get viewport information

Once you confirm that the browser supports the Visual Viewport API, we can get the detailed information of the viewport through the following code:

if ('visualViewport' in window) {
    const viewport = ;
    (`Viewport width: ${}`);
    (`Viewport height: ${}`);
    (`Scaling: ${}`);
    (`Left offset: ${}`);
    (`Up offset: ${}`);
}

Monitoring viewport changes

The size and position of the viewport may vary due to user operations (such as scrolling, scaling). We can monitor these changes by adding event listeners:

if ('visualViewport' in window) {
    const viewport = ;

    ('resize', () => {
        ('Viewport size changed');
        (`New viewport width: ${}`);
        (`New viewport height: ${}`);
    });

    ('scroll', () => {
        ('Viewport position changed');
        (`New left offset: ${}`);
        (`Newly uploaded offset: ${}`);
    });
}

Sample Application

Here is a simple example application that shows how to use the Visual Viewport API to adjust the position of an element so that it is always in the center of the viewport:

<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Visual Viewport Example</title>
    <style>
        #centerBox {
            position: absolute;
            width: 100px;
            height: 100px;
            background-color: red;
        }
    </style>
</head>
<body>
    <div ></div>
    <script>
        if ('visualViewport' in window) {
            const viewport = ;
            const box = ('centerBox');

            function updateBoxPosition() {
                const centerX =  +  / 2;
                const centerY =  +  / 2;
                 = `${centerX -  / 2}px`;
                 = `${centerY -  / 2}px`;
            }

            ('resize', updateBoxPosition);
            ('scroll', updateBoxPosition);

            updateBoxPosition();
        }
    </script>
</body>
</html>

in conclusion

The Visual Viewport API provides developers with a powerful and flexible way to manage and obtain viewport information. By using this API, we can more accurately control page layout and respond to user interactions, improving user experience. In practical applications, the rational use of the Visual Viewport API can help us solve many problems encountered in mobile devices and multi-screen environments. Hope this article helps you better understand and use the Visual Viewport API.

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