Super practical! JavaScript modifies CSS variables to achieve the purpose of dynamically modifying styles

In web development, we usually use CSS to set the style of web pages. However, in the development process, sometimes we need to dynamically modify the style according to different conditions. At this time, we need to use JavaScript to achieve it.

In CSS, there is a concept of variables, which can be used to define style attributes such as color and font size. In this article, we will introduce how to use JavaScript to modify CSS variables to dynamically modify styles.

Case presentation:

We assume that there is a button that, when clicked, will change the background color of all paragraphs in the page. First, we need to define a variable in CSS to represent the background color. In this example, we define the variable name as --bg-color.

	:root {
	  --bg-color: #ffffff;
	}
	
	p {
	  background-color: var(--bg-color);
	}

In the code above, we use :root to define the global CSS variable --bg-color and set it to white. We then set the background color of all paragraphs to the --bg-color variable.

Next, we will use JavaScript to dynamically modify the value of the --bg-color variable. We'll add a click event listener that, when the button is clicked, will randomly generate a color value and set it as the value of --bg-color .

const button = document.querySelector('button');
button.addEventListener('click', () => {
  document.documentElement.style.setProperty('--bg-color', 'red');
});

In the above code, we have successfully modified CSS variables dynamically through JavaScript, realizing the effect of dynamically modifying styles. When we click the button, the background color of all paragraphs in the page will change to red.

Summarize

JavaScript can modify CSS variables to achieve the effect of dynamically modifying styles, which is very suitable for use in scenarios that need to dynamically change styles. For example, when a user performs certain operations on a website and needs to dynamically change the style of the page according to different conditions, JavaScript can be used to modify CSS variables.

In addition, CSS variables can also help us better organize and manage code. By using variables, we can avoid repeatedly defining the same value in multiple style properties, making the code more readable and maintainable.

However, it should be noted that CSS variables are not supported by all browsers. CSS variables may not be parsed and used correctly in some older browsers. Therefore, when using CSS variables, a compatibility test is required, and use and adjustments should be made according to the actual situation.

Also, the scope of CSS variables needs attention. The scope defined by a CSS variable is only valid in the element defining the variable and its descendants . If you need to use this variable in the whole page, you can define it in :root.