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 v2.0.0 up to v2.2.4, support for newer version will be added continuously
Works in Node >=12 and all modern browsers
Fully typed
4.1 kB minified + gzipped

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 = `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 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('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 hte MySlightlyModifiedInput, the input now only renders the class p-3.

Features

Optimized for speed

I didn't run any performance benchmarks so far, but you should be able to merge a lot of classes per second. Some aspects of the library:

Results get cached by default, so you don't need to worry about wasteful rerenders. The library uses a LRU cache which stores 500 different results. The cache size can be modified or being opt-out of by using createTailwinfMerge().
Expensive computations of data structures happen on demand.

Last conflicting class wins

twMerge('p-5 p-2 p-4') // → 'p-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'

API reference

Reference to all exports of tailwind-merge.

`twMerge`

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

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 with a common start in all class names
        dynamicClasses: {
            ...defaultConfig.dynamicClasses,
            // ↓ It's important that keys at this level don't have dashes in them.
            foo: [
                // ↓ Creates group of classes which have conflicting styles
                //   Classes here: foo-1, foo-2, foo-bar-baz-1, foo-bar-baz-2
                ['1', '2', { 'bar-baz': ['1', '2'] }],
            ],
            bar: [
                // ↓ Another group with classes bar-auto, bar-1000, bar-1001, …
                ['auto', (value) => Number(value) > 1000],
            ],
        },
        // ↓ Same like `dynamicClasses`, just for classes with no common starting characters
        standaloneClasses: [
            ...defaultConfig.standaloneClasses,
            // ↓ Same structure like in `dynamicClasses`, but only strings allowed
            ['my-custom-class', 'other-class-same-group'],
        ],
        // ↓ Here you can define additional conflicts across different groups
        conflictingGroups: {
            ...defaultConfig.conflictingGroups,
            // ↓ Path to class group which creates a conflict with …
            'dynamicClasses.foo.0': [
                // ↓ … classes from group at this path
                'dynamicClasses.bar.0',
            ],
        },
    }
})

KeKs0r/tailwind-merge