How to change css style with js

With the development of Web technology, JavaScript (JS) has become an indispensable part of Web development. JS can add dynamic effects to web pages, change the interactive experience between users and the page, and can also change the appearance of the page by manipulating CSS styles.

In this article, we will learn how to change CSS styles using JS. Let’s understand it step by step.

1. Operation style attribute

Each HTML element has a style attribute, which is used to set the CSS style of the element. We can use JS to modify the value of the style attribute to change the element style. For example, to change the background color of an element, you can use the following code:

document.getElementById("elementId").style.backgroundColor = "red";

Note that this code assumes that the element has an id attribute and that JS will find the element through the getElementById() method. We can use this method for any element, for example use the following code to change the font size of a paragraph:

document.getElementsByTagName("p")[0].style.fontSize = "24px";

This code uses the getElementsByTagName() method to select the first paragraph of the page and set the font size to 24 pixels.

2. Operation classList attribute

In addition to the style attribute, HTML elements also have a classList attribute, which is a DOMTokenList object that contains all class names of the element. Classes can be used to change the appearance of an element, such as changing the element's background image or adding animation effects.

We can use add() to add a class to an element and remove() to delete a class, for example:

document.getElementById("elementId").classList.add("newClass");
document.getElementById("elementId").classList.remove("oldClass");

In this example, we will add A new class newClass, and then delete the old class oldClass.

3. Manipulate multiple values ​​​​in the style attribute

In some cases, we may need to change multiple attributes of the style, such as the position, size and color. To achieve this, we can define multiple values ​​in the style attribute. For example, the following code sets the width, height, background color, and position of the element:

document.getElementById("elementId").style.cssText = "width: 100px; height: 50px; background-color: red; position: absolute; top: 10px; left: 10px;";

Here, we have used the cssText property to specify multiple CSS properties for the element. We can include any valid CSS property in this string to change any style of the element.

4. Use classList.toggle() to switch classes

We can use the toggle() method provided by classList to switch between two classes. For example, the following code will switch the element class from "oldClass" to "newClass" on mouse click:

document.getElementById("elementId").addEventListener("click", function() {
    this.classList.toggle("oldClass");
    this.classList.toggle("newClass");
});

Here, we add a click event to the element with elementId. When the user clicks on the element, the toggle() method removes the "oldClass" class from the element and adds the "newClass" class, then switches back to the "oldClass" class on the next click.

By manipulating CSS styles with JavaScript, we can create various interactive effects and dynamic web page layouts. Remember, when operating CSS styles, you must choose an appropriate way to operate style attributes to achieve the best results.

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