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Element: className property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨July 2015⁩.

The className property of the Element interface gets and sets the value of the class attribute of the specified element.

Value

A string variable representing the class or space-separated classes of the current element.

Examples

const el = document.getElementById("item");
el.className = el.className === "active" ? "inactive" : "active";

Notes

The name className is used for this property instead of class because of conflicts with the "class" keyword in many languages which are used to manipulate the DOM.

className can also be an instance of SVGAnimatedString if the element is an SVGElement. It is easier to get/set the class attribute of an element using Element.getAttribute and Element.setAttribute if you are dealing with SVG elements. However, take into account that Element.getAttribute returns null instead of "" if the element has an empty class attribute.

elm.setAttribute("class", "my-class");
const myClass = elm.getAttribute("class");

Note: class is the name of an HTML Attribute, while className is the name of a DOM Property.

Specifications

Specification
DOM> # ref-for-dom-element-classname①>

Browser compatibility