js dynamically modify css

With the continuous development of front-end technology, JavaScript has become an indispensable part of web development. In JavaScript, dynamically modifying CSS styles is one of the common requirements. It can achieve many cool effects, such as special effects when the mouse is hovering, and the navigation bar color changes when the page is scrolled. This article will introduce in detail how to dynamically modify CSS styles in JavaScript.

1. Use JavaScript to modify the style of elements

In HTML, we can beautify the page by adding CSS styles to elements. In JavaScript, the effect of dynamically modifying styles can be achieved by modifying the attributes of elements.

1. Using the style attribute of the element

We can use the style attribute of the HTML element to directly modify the style of the element. This method is suitable for modifying the style of a single element.

Sample code:

我是一段文本

In JavaScript, you can dynamically modify its style by getting the style attribute of an element:

var box = document.querySelector('#box');
box.style.backgroundColor = 'red';

After modifying its style through JavaScript, the style of the element will turn red.

2. Using the element's style element

Another way to dynamically modify the style of an element is to use the element's style element. The style element allows us to directly access the element's style sheet in JavaScript and modify its style.

Sample code:

In JavaScript, you can get the style element by getting the style attribute of the element, and then dynamically modify its style:

var box = document.querySelector('#box');
var styles = box.style;

// 修改样式
styles.backgroundColor = 'red';

Modify it through JavaScript After styling, the element's style will turn red.

2. Use classList to modify the style

The two methods introduced above are suitable for modifying the style of a single element. If we need to control the styles of multiple elements on the web page at will, then these two methods This method seems too troublesome. At this point, we can use the classList attribute to dynamically modify the style.

1. Add and delete class

The classList attribute contains many convenient methods that allow us to easily add and delete classes. With classes, we can define a set of styles for an element and add or remove them dynamically via JavaScript.

Sample code:

我是一段文本

In JavaScript, you can add or remove classes for elements through the add() and remove() methods of classList:

var box = document.querySelector('.box');
box.classList.add('red');
box.classList.remove('box');

Modify through JavaScript After it is styled, the element's style will turn red, and the element's box class will be deleted.

2. Toggle class

In addition to the add() and remove() methods, classList also has a convenient method called toggle(). The toggle() method can switch the class of the element. If the class already exists in the element, the method will delete the class, otherwise it will add the class.

Sample code:

我是一段文本

In JavaScript, you can switch the class of an element through the toggle() method of classList:

var box = document.querySelector('.box');
box.classList.toggle('red');
box.classList.toggle('green');

After modifying its style through JavaScript, the element's class The style will change from red to green.

3. Directly modify the style sheet

The above method can control the style of a single element or multiple elements, but if you need to directly modify the style sheet, you need to use a different method.

In JavaScript, a style sheet is represented as an object, and we can dynamically modify the styles in it through JavaScript code to achieve dynamic modification of the style sheet.

Sample code:

我是一段文本

In JavaScript, you can dynamically modify its style by obtaining the object corresponding to the style sheet:

var styleSheet = document.styleSheets[0];
var rules = styleSheet.cssRules || styleSheet.rules;

for (var i = 0; i < rules.length; i++) {
    var rule = rules[i];
    if (rule.selectorText === '.box') {
        rule.style.backgroundColor = 'red';
    }
}

After modifying its style through JavaScript, the element's style The style will turn red.

4. Summary

This article introduces three methods of dynamically modifying CSS styles, including using the style attribute of the element, using the style element of the element, and using classList. In addition, in order to meet the need to directly modify the style sheet, we also introduced the method of directly modifying the style sheet. These methods allow us to easily implement the function of dynamically modifying CSS styles in JavaScript.

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