How to set css properties in js

JavaScript is a very popular web programming language that helps developers create more dynamic and interactive websites. Among them, setting CSS properties is an important aspect in JavaScript, allowing us to dynamically change the style of HTML elements. This article will detail how to set CSS properties using JavaScript.

1. How to use JavaScript to set CSS properties

To use JavaScript to set CSS properties, you need to use the following two methods:

1. Use the style attribute

For HTML elements, you can use the style attribute in JavaScript to set CSS attributes. In this way, we can get or set the style rules of an element.

The following is a sample code:

//访问元素的样式属性
var element = document.getElementById("example");
var backgroundColor = element.style.backgroundColor;

//修改元素的样式属性
element.style.backgroundColor = "#f0f";

In the above code, we first obtain an element named "example" and read its background color. Next, we changed its background color to '#f0f', which is pink.

Please note that the disadvantage of using the style attribute is that each style attribute needs to be set manually. Therefore, if you want to set multiple properties, you may need to write a lot of code.

2. Use the classList attribute

Through the classList attribute, we can access the element class list and can add or remove classes to change the style of the element. The classList attribute is an attribute on the HTML element. It contains a DOMTokenList object that stores all the class names of the element.

The following is an example code for adding a class to an element:

var element = document.getElementById("example");
element.classList.add("new-class");

In the above code, we add a class named "new-class" to the element with the ID "example" superior. Now, we can define styles for "new-class" classes in a CSS file and apply the styles dynamically via JavaScript at runtime.

2. Practical use cases of applying JavaScript to set CSS properties

Using JavaScript to set CSS properties is a very useful technology that can come in handy in many ways. Here are some practical use cases:

1. Interactive forms

With JavaScript, we can dynamically change the style of form elements, as well as check whether the form has been filled out correctly before it is submitted.

For example, we can read values ​​from form inputs and change the style of form elements based on specific rules. For example, if a required field is not filled in by the user, you can style the text box red to indicate to the user that the field is not filled in.

2. Dynamic page effects

Dynamic page effects can be created using JavaScript. For example, when a user hovers over a button, we can trigger an animation effect to grab the user's attention.

We can also use JavaScript to dynamically change image size and position and create complex transition effects by adding or removing classes.

3. Responsive design

Responsive design is a design method that provides the best user experience on different devices. Using JavaScript, we can modify the layout of a web page based on the current window size and change element size and position to fit the screen size.

For example, we can hide certain elements on small screens to improve the readability of the page or ignore some complex graphic effects to improve web page performance.

3. Summary

This article introduces two different methods of setting CSS properties using JavaScript and provides some practical use cases. In web development, using JavaScript to set CSS properties is a very useful technique that can help us create more dynamic and interactive websites.

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