recipes.md

Recipes

How to configure tailwind-merge with some common patterns.

Adding custom scale from Tailwind config to tailwind-merge config

I have a custom shadow scale with the keys 100, 200 and 300 configured in Tailwind. How do I make tailwind-merge resolve conflicts among those?

We'll be able to do this by creating a custom twMerge functon with extendTailwindMerge.

First, we need to know whether we want to override or extend the default scale. Let's say we extended the default config by putting the scale into the extend key in the Tailwind config.

Then we check whether our particular theme scale is included in tailwind-merge's theme config object here. In the hypothetical case that tailwind-merge supported Tailwind's boxShadow theme scale, we could add it to the tailwind-merge config like this:

const customTwMerge = extendTailwindMerge({
    extend: {
        theme: {
            // The `boxShadow` key isn't actually supported
            boxShadow: [{ shadow: ['100', '200', '300'] }],
        },
    },
})

In the case of the boxShadow scale, tailwind-merge doesn't include it in the theme object. Instead, we need to check out the default config of tailwind-merge and search for the class group ID of the box shadow scale. After a quick search we find that tailwind-merge is using the key shadow for that group. We can add our custom classes to that group like this:

const customTwMerge = extendTailwindMerge({
    extend: {
        classGroups: {
            shadow: [{ shadow: ['100', '200', '300'] }],
        },
    },
})

Note that by using the extend object we're only adding our custom classes to the existing ones in the config, so twMerge('shadow-200 shadow-lg') will return the string shadow-lg. If we want to override the class instead, we need to use the override object instead.

Extracting classes with Tailwind's @apply

How do I make tailwind-merge resolve conflicts with a custom class created with @apply?

.btn-primary {
    @apply py-2 px-4 bg-blue-500 text-white rounded-lg hover:bg-blue-700;
}

I don't recommend using Tailwind's @apply directive for classes that might get processed with tailwind-merge.

tailwind-merge would need to be configured so that it knows about which classes .btn-primary is in conflict with. This means: If someone adds another Tailwind class to the @apply directive, the tailwind-merge config would need to get modified accordignly, keeping it in sync with the written CSS. This easy-to-miss dependency is fragile and can lead to bugs with incorrect merging behavior.

Instead of creating custom CSS classes, I recommend keeping the collection of Tailwind classes in a string variable in JavaScript and access it whenever you want to apply those styles. This way you can reuse the collection of styles but don't need to touch the tailwind-merge config.

// React components with JSX syntax used in this example

const BTN_PRIMARY_CLASSNAMES = 'py-2 px-4 bg-blue-500 text-white rounded-lg hover:bg-blue-700'

function ButtonPrimary(props) {
    return <button {...props} className={twMerge(BTN_PRIMARY_CLASSNAMES, props.className)} />
}

Modifying inputs and output of twMerge

How do I make twMerge accept the same argument types as clsx/classnames?

You can wrap twMerge in another function which can modify the inputs and/or output.

function customTwMerge(...inputs) {
    const modifiedInputs = modifyInputs(inputs)
    return twMerge(modifiedInputs)
}

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