CSS Object Model (CSSOM)

May 20, 2023

The CSS Object Model (CSSOM) is a JavaScript API that provides access to the stylesheets and their corresponding CSS rules that are applied to an HTML document. The CSSOM allows web developers to manipulate, create and modify CSS styles dynamically using JavaScript, making web page styling more interactive and responsive.


The purpose of the CSS Object Model is to provide a standardized way of accessing and manipulating CSS styles dynamically. Prior to the development of CSSOM, the only way to modify CSS styles in real-time was to use JavaScript to directly manipulate the styles of individual HTML elements. This approach was highly error-prone and resulted in spaghetti code that was difficult to maintain and scale.

With CSSOM, developers can access and modify the stylesheets and corresponding CSS styles that are applied to individual HTML elements. This allows them to create more modular and maintainable code that can be easily extended and adapted to different use cases.

CSSOM is also beneficial for performance optimizations. By accessing and modifying the CSS styles directly, developers can avoid expensive document reflows that occur when styles are applied to individual HTML elements. This can significantly improve the performance of web applications, especially those that make heavy use of CSS animations and transitions.


The CSS Object Model is used extensively in modern web development, particularly in front-end web development. With CSSOM, developers can dynamically manipulate the styling of individual elements, allowing them to create interactive and responsive user interfaces.

One common use case for CSSOM is creating dynamic user interfaces. For example, developers can use CSSOM to change the styling of a button when it is hovered over, or to add/remove classes from a navigation menu based on user interactions. This can provide a more intuitive and seamless user experience, improving the overall usability of web applications.

CSSOM is also used extensively in the development of responsive web design. With CSSOM, developers can create media queries that adapt to different screen sizes and device types, allowing them to create responsive layouts that adjust to the user’s device. This is particularly important in today’s mobile-first world, where more and more users are accessing the web from mobile devices with varying screen sizes.

Another common use case for CSSOM is in the development of CSS frameworks and libraries. Frameworks such as Bootstrap and Foundation make extensive use of CSSOM to provide pre-defined styles that can be easily customized and extended. This allows developers to create rich and varied user interfaces without having to write all of the CSS code from scratch.


It’s important to note that the CSS Object Model is distinct from the Document Object Model (DOM), which is also a JavaScript API that provides access to the elements and content of an HTML document. While the DOM provides access to the HTML structure of a document, the CSSOM provides access to the styles that are applied to those elements.

While the two APIs are separate, they are closely related, and both are used extensively in modern web development. In fact, modern web applications often make heavy use of both the DOM and CSSOM in order to create rich and dynamic user interfaces.

Browser Support

The CSS Object Model is supported by all modern web browsers, including Chrome, Firefox, Safari, and Edge. However, support for some of the newer features of the API may vary between browsers, so it’s important to test your code on multiple browsers to ensure cross-browser compatibility.