JavaScript modifies external css

JavaScript is a powerful programming language with a wide range of applications. In web development, JavaScript is often used to modify the behavior and style of a page. In this article, we will focus on how to modify external CSS using JavaScript.

First, let’s understand what external CSS is. Typically, a website's CSS style sheet is stored in a separate file, which makes the HTML file more concise and easier to maintain. This CSS file is referenced in the HTML file as follows:

<link href="style.css" rel="stylesheet" type="text/css">

The above code will introduce the style.css file into the HTML page as an external CSS style sheet.

So, how to use JavaScript to operate this external CSS file? Below are the two main methods.

1. Use JavaScript to modify the href attribute of the link tag

We can obtain the link tag through JavaScript and modify its href attribute to change the style sheet.

First, the way to get the link tag can be achieved through the following code:

var links = document.getElementsByTagName('link');

Then, we can traverse all the link tags and find the one we want to change:

for (var i = 0; i < links.length; i++) {
  if (links[i].getAttribute('href').indexOf('style.css')!=-1) {
    links[i].setAttribute('href', 'new-style.css');
  }
}

In the above code, we first use a loop to traverse all link tags and determine whether it is the style sheet link we want to modify. If so, we use the setAttribute method to modify its href attribute to a new link, thereby changing the style sheet.

2. Directly modify the CSS rules of the style sheet

The second method is to directly modify the CSS rules of the style sheet. In this method, we need to obtain the style sheet object first, and then modify the CSS rules to achieve the effect of changing the style.

We can use document.styleSheets to get all style sheet objects on the page. We can then use the insertRule or deleteRule methods to add or delete CSS rules, thereby modifying the page's style.

var styleSheet = document.styleSheets[0];  // 获取第一个样式表对象
styleSheet.insertRule('body { background-color: #f5f5f5; }', 0); // 添加一个新的 CSS 规则
styleSheet.deleteRule(0);  // 删除第一个 CSS 规则

In the above code, we first get the first style sheet object, and then use the insertRule method to add a new CSS rule, that is, the background of body Change the color to #f5f5f5. Next, we delete the first CSS rule using the deleteRule method.

Summary

Through the above two methods, we can easily use JavaScript to modify the external CSS style sheet, thereby changing the style of the page. Of course, this is only a brief introduction to JavaScript's manipulation of style sheets. In fact, JavaScript has more CSS manipulation methods and methods available for use.

No matter which method is used, we need to conduct sufficient testing and verification to ensure that modifying the style sheet can take effect smoothly and will not affect other styles. At the same time, we must also pay attention to compatibility issues. Different browsers have different support levels and methods for JavaScript operation style sheets.

In practice, how to choose the appropriate method depends on the specific needs and scenarios. We need to determine which method is more appropriate based on the actual situation.

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