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A simple utility for conditionally joining classNames together


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Package description

What is classnames?

The classnames package is a simple utility for conditionally joining class names together. It is commonly used in React projects but can be used anywhere that requires dynamic class name computation.

What are classnames's main functionalities?

String arguments

Combine multiple string arguments into one class name.

classnames('foo', 'bar'); // 'foo bar'

Object arguments

Use an object to include class names conditionally based on the truthiness of the object's values.

classnames({ 'foo': true, 'bar': false }); // 'foo'

Array arguments

Pass an array of class names which will be joined together.

classnames(['foo', 'bar']); // 'foo bar'

Mixed arguments

Combine string, object, and array arguments to form a class name string.

classnames('foo', { 'bar': true, 'duck': false }, ['baz', { 'quux': true }]); // 'foo bar baz quux'

Other packages similar to classnames



v2.3.2 / 2022-09-13

  • Fix TypeScript types when using require, thanks Mark Dalgleish (#276)
  • Fix toString as [Object object] in a vm, thanks Remco Haszing (#281)




NPM version Node.js CI NPM Weekly Downloads License Supported by Thinkmill

A simple JavaScript utility for conditionally joining classNames together.

Install with npm, Bower, or Yarn:

# via npm
npm install classnames

# via Bower
bower install classnames

# or Yarn (note that it will automatically save the package to your `dependencies` in `package.json`)
yarn add classnames

Use with Node.js, Browserify, or webpack:

var classNames = require('classnames');
classNames('foo', 'bar'); // => 'foo bar'

Alternatively, you can simply include index.js on your page with a standalone <script> tag and it will export a global classNames method, or define the module if you are using RequireJS.

Project philosophy

We take the stability and performance of this package seriously, because it is run millions of times a day in browsers all around the world. Updates are thoroughly reviewed for performance impacts before being released, and we have a comprehensive test suite.

Classnames follows the SemVer standard for versioning.

There is also a Changelog.


The classNames function takes any number of arguments which can be a string or object. The argument 'foo' is short for { foo: true }. If the value associated with a given key is falsy, that key won't be included in the output.

classNames('foo', 'bar'); // => 'foo bar'
classNames('foo', { bar: true }); // => 'foo bar'
classNames({ 'foo-bar': true }); // => 'foo-bar'
classNames({ 'foo-bar': false }); // => ''
classNames({ foo: true }, { bar: true }); // => 'foo bar'
classNames({ foo: true, bar: true }); // => 'foo bar'

// lots of arguments of various types
classNames('foo', { bar: true, duck: false }, 'baz', { quux: true }); // => 'foo bar baz quux'

// other falsy values are just ignored
classNames(null, false, 'bar', undefined, 0, 1, { baz: null }, ''); // => 'bar 1'

Arrays will be recursively flattened as per the rules above:

var arr = ['b', { c: true, d: false }];
classNames('a', arr); // => 'a b c'

Dynamic class names with ES2015

If you're in an environment that supports computed keys (available in ES2015 and Babel) you can use dynamic class names:

let buttonType = 'primary';
classNames({ [`btn-${buttonType}`]: true });

Usage with React.js

This package is the official replacement for classSet, which was originally shipped in the React.js Addons bundle.

One of its primary use cases is to make dynamic and conditional className props simpler to work with (especially more so than conditional string manipulation). So where you may have the following code to generate a className prop for a <button> in React:

class Button extends React.Component {
  // ...
  render () {
    var btnClass = 'btn';
    if (this.state.isPressed) btnClass += ' btn-pressed';
    else if (this.state.isHovered) btnClass += ' btn-over';
    return <button className={btnClass}>{this.props.label}</button>;

You can express the conditional classes more simply as an object:

var classNames = require('classnames');

class Button extends React.Component {
  // ...
  render () {
    var btnClass = classNames({
      btn: true,
      'btn-pressed': this.state.isPressed,
      'btn-over': !this.state.isPressed && this.state.isHovered
    return <button className={btnClass}>{this.props.label}</button>;

Because you can mix together object, array and string arguments, supporting optional className props is also simpler as only truthy arguments get included in the result:

var btnClass = classNames('btn', this.props.className, {
  'btn-pressed': this.state.isPressed,
  'btn-over': !this.state.isPressed && this.state.isHovered

Alternate dedupe version

There is an alternate version of classNames available which correctly dedupes classes and ensures that falsy classes specified in later arguments are excluded from the result set.

This version is slower (about 5x) so it is offered as an opt-in.

To use the dedupe version with Node.js, Browserify, or webpack:

var classNames = require('classnames/dedupe');

classNames('foo', 'foo', 'bar'); // => 'foo bar'
classNames('foo', { foo: false, bar: true }); // => 'bar'

For standalone (global / AMD) use, include dedupe.js in a <script> tag on your page.

Alternate bind version (for css-modules)

If you are using css-modules, or a similar approach to abstract class "names" and the real className values that are actually output to the DOM, you may want to use the bind variant.

Note that in ES2015 environments, it may be better to use the "dynamic class names" approach documented above.

var classNames = require('classnames/bind');

var styles = {
  foo: 'abc',
  bar: 'def',
  baz: 'xyz'

var cx = classNames.bind(styles);

var className = cx('foo', ['bar'], { baz: true }); // => "abc def xyz"

Real-world example:

/* components/submit-button.js */
import { Component } from 'react';
import classNames from 'classnames/bind';
import styles from './submit-button.css';

let cx = classNames.bind(styles);

export default class SubmitButton extends Component {
  render () {
    let text = ? 'Processing...' : 'Submit';
    let className = cx({
      base: true,
      disabled: this.props.form.valid,
    return <button className={className}>{text}</button>;

Polyfills needed to support older browsers

classNames >=2.0.0

Array.isArray: see MDN for details about unsupported older browsers (e.g. <= IE8) and a simple polyfill.


Copyright (c) 2018 Jed Watson. Copyright of the Typescript bindings are respective of each contributor listed in the definition file.



Last updated on 13 Sep 2022

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