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tailwind-merge

Utility function to efficiently merge Tailwind CSS classes in JS without style conflicts.

import { twMerge } from 'tailwind-merge'

twMerge('px-2 py-1 bg-red hover:bg-dark-red', 'p-3 bg-[#B91C1C]')
// → 'hover:bg-dark-red p-3 bg-[#B91C1C]'
  • Supports Tailwind v2.0 up to v2.2, support for newer versions will be added continuously
  • Works in Node >=12 and all modern browsers
  • Fully typed
  • 4.8 kB minified + gzipped (96.3% self, 3.7% hashlru)

Early development

This library is in an early pre-v1 development stage and might have some bugs and inconveniences here and there. I use the library in production and intend it to be sufficient for production use, as long as you're fine with some potential breaking changes in minor releases until v1 (lock the version range to patch releases with ~ in your package.json to prevent accidental breaking changes).

I want to keep the library on v0 until I feel confident enough that there aren't any major bugs or flaws in its API and implementation. If you find a bug or something you don't like, please submit an issue or a pull request. I'm happy about any kind of feedback!

What is it for

If you use Tailwind with a component-based UI renderer like React or Vue, you're probably familiar with this situation:

import React from 'react'

function MyGenericInput(props) {
    const className = `border rounded px-2 py-1 ${props.className || ''}`
    return <input {...props} className={className} />
}

function MySlightlyModifiedInput(props) {
    return (
        <MyGenericInput
            {...props}
            className="p-3" // ← Only want to change some padding
        />
    )
}

When the MySlightlyModifiedInput is rendered, an input with the className border rounded px-2 py-1 p-3 gets created. But because of the way the CSS cascade works, the styles of the p-3 class are ignored. The order of the classes in the className string doesn't matter at all and the only way to apply the p-3 styles is to remove both px-2 and py-1.

This is where tailwind-merge comes in.

function MyGenericInput(props) {
    // ↓ Now `props.className` can override conflicting classes
    const className = twMerge('border rounded px-2 py-1', props.className)
    return <input {...props} className={className} />
}

tailwind-merge makes sure to override conflicting classes and keeps everything else untouched. In the case of the MySlightlyModifiedInput, the input now only renders the classes border rounded p-3.

Features

Optimized for speed

  • Results get cached by default, so you don't need to worry about wasteful rerenders. The library uses a LRU cache which stores up to 500 different results. The cache size can be modified or opt-out of by using createTailwindMerge().
  • Expensive computations happen upfront so that twMerge() calls without a cache hit stay fast.
  • These computations are called lazily on the first call to twMerge() to prevent it from impacting app startup performance if it isn't used initially.

Last conflicting class wins

twMerge('p-5 p-2 p-4') // → 'p-4'

Allows refinements

twMerge('p-3 px-5') // → 'p-3 px-5'
twMerge('inset-x-4 right-4') // → 'inset-x-4 right-4'

Resolves non-trivial conflicts

twMerge('inset-x-px -inset-1') // → '-inset-1'
twMerge('bottom-auto inset-y-6') // → 'inset-y-6'
twMerge('inline block') // → 'block'

Supports prefixes and stacked prefixes

twMerge('p-2 hover:p-4') // → 'p-2 hover:p-4'
twMerge('hover:p-2 hover:p-4') // → 'hover:p-4'
twMerge('hover:focus:p-2 focus:hover:p-4') // → 'focus:hover:p-4'

Supports custom values

twMerge('bg-black bg-[color:var(--mystery-var)]') // → 'bg-[color:var(--mystery-var)]'
twMerge('grid-cols-[1fr,auto] grid-cols-2') // → 'grid-cols-2'

Supports important modifier

twMerge('!p-3 !p-4 p-5') // → '!p-4 p-5'
twMerge('!right-2 !-inset-x-1') // → '!-inset-x-1'

Preserves non-Tailwind classes

twMerge('p-5 p-2 my-non-tailwind-class p-4') // → 'my-non-tailwind-class p-4'

Supports custom colors out of the box

twMerge('text-red text-secret-sauce') // → 'text-secret-sauce'

Ignores undefined, null and false values

twMerge('some-class', undefined, null, false) // → 'some-class'

API reference

Reference to all exports of tailwind-merge.

twMerge

function twMerge(...classLists: Array<string | undefined | null | false>): string

Default function to use if you're using the default Tailwind config or are close enough to the default config. You can use this function if all of the following points apply to your Tailwind config:

  • Only using variants known to Tailwind
  • Only using default color names or color names which don't clash with Tailwind class names
  • Only deviating by number values from number-based Tailwind classes

If some of these points don't apply to you, it makes sense to test whether twMerge() still works as intended with your custom classes. Otherwise, you can create your own custom merge function with createTailwindMerge().

createTailwindMerge

function createTailwindMerge(createConfig: CreateConfig): TailwindMerge

Function to create merge function with custom config.

You need to provide a function which resolves to the config tailwind-merge should use for the new merge function. You can either extend from the default config or create a new one from scratch.

// ↓ Callback passed to `createTailwindMerge()` is called when
//   `customTwMerge()` gets called the first time.
const customTwMerge = createTailwindMerge((getDefaultConfig) => {
    const defaultConfig = getDefaultConfig()

    return {
        cacheSize: 0, // ← Disabling cache
        prefixes: [
            ...defaultConfig.prefixes,
            'my-custom-prefix', // ← Adding custom prefix
        ],
        // ↓ Here you define class groups
        classGroups: {
            ...defaultConfig.classGroups,
            // ↓ The `foo` key here is the class group ID
            //   ↓ Creates group of classes which have conflicting styles
            //     Classes here: foo, foo-2, bar-baz, bar-baz-1, bar-baz-2
            foo: ['foo', 'foo-2', { 'bar-baz': ['', '1', '2'] }],
            //   ↓ Another group with classes qux-auto, qux-1000, qux-1001, …
            bar: [{ qux: ['auto', (value) => Number(value) >= 1000] }],
        },
        // ↓ Here you can define additional conflicts across different groups
        conflictingClassGroups: {
            ...defaultConfig.conflictingClassGroups,
            // ↓ ID of class group which creates a conflict with …
            //     ↓ … classes from groups with these IDs
            foo: ['bar'],
        },
    }
})

Versioning

This package follows the SemVer versioning rules. More specifically:

  • Patch version gets incremented when unintended behaviour is fixed which doesn't break any existing API. Note that bug fixes can still alter which styles are applied. E.g. a bug gets fixed in which the conflicting classes inline and block weren't merged correctly so that both would end up in the result.

  • Minor version gets incremented when additional features are added which don't break any existing API. However, a minor version update might still alter which styles are applied if you use Tailwind features not yet supported by tailwind-merge. E.g. a new Tailwind prefix magic gets added to this package which changes the result of twMerge('magic:px-1 magic:p-3') from magic:px-1 magic:p-3 to magic:p-3.

  • Major version gets incremented when breaking changes are introduced to the package API. E.g. the return type of twMerge() changes.

  • alpha releases might introduce breaking changes on any update. Whereas beta releases only introduce new features or bug fixes.

  • Releases with major version 0 might introduce breaking changes on a minor version update.

  • A changelog is documented in GitHub Releases.