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classnames

by JedWatson

JedWatson /classnames

A simple javascript utility for conditionally joining classNames together

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Classnames

NPM version Build status 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
 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.

Usage

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
 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 {this.props.label};
  }
}

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 {this.props.label}; } }

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
 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 = this.props.store.submissionInProgress ? 'Processing...' : 'Submit'; let className = cx({ base: true, inProgress: this.props.store.submissionInProgress, error: this.props.store.errorOccurred, disabled: this.props.form.valid, }); return {text}; } };

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.

License

MIT. Copyright (c) 2018 Jed Watson.

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