Convert mixins into composables to reuse them in Composition API

• helpful during Options API -> Composition API migrations / in mixed code-bases
• simple API - one function call is all you need
• TS Support (with small caveats)
• small footprint:

// given an existing mixin such as this:
export const messageMixin  = {
    data() {
        return {
            msg: 'Hello World'
        }
    },
    computed: {
        loudMsg() {
            return this.capitalize(this.msg)   '!!!1eleven!'
        }
    },
    methods: {
        capitalize(value) { return value.toUpperCase() }
    } 
}

// we can create a composable from it with a single function call
import { createComposableFromMixin } from 'vue-mixable'
export const useMessage = createComposableFromMixin(messageMixin)

This composable can then be used in setup()/ <script setup>:

<script setup>
const {
    msg, // ref
    loudMsg, // computed() ref
    capitalize // function
} = useMessage()
</script>

This library is primarily useful for developers trying to migrate a Options-API codebase using Mixins for code sharing to Composition API using composables for code sharing.

One of the challenges in such a migration is that one often cannot rewrite a mixin into a composable and replace all of that mixin's usage instances in the app at once, epsecially when mixins depend on one another, which is often the case in larger code-bases.

This is where vue-mixable can help: The team can keep all their mixins for the time of the migration, but convert each of them into composables with one line of code. You get have your cake, and eat it to, in a way.

Then they can migrate individual components from the mixin to the composable at their own pace, and once the migration is done, they can rewrite the mixin into a proper standalone composable and finally remove the mixin from your codebase.

npm install vue-mixable

vue-mixable provides full support for mixins that use the following Options APIs

• data
• computed
• methods
• watch
• provide
• inject
• props (see Note in the next section)
• emits (see Note in the next section)

Options with no direct support (currently):

• inheritAttrs
• components
• directives
• name

If you use any of the above options, you would have to set them manually in any component that uses the generated composable instead of the original mixin.

Mixins can contain props definitions. Composables cannot, as they are functions invoked during component initialization (in setup(), at which point props must have been defined already.

vue-mixable solves with in the following way:

const mixin = {
    props: ['modelValue', 'age', 'street', 'city'],
    emits: ['modelValue:update', 'certified']
    // ...and other mixin content, i.e.:
    data: () => ({
        //...
    })
}

export const usePerson = createComposableFromMixin(mixin)
// props and emits options will be available 
// as properties on the composable function(!)
usePerson.props // => ['modelValue', 'age', 'street', 'city']
usePerson.emits // => ['modelValue:update', 'certified']

Usage

import { usePerson } from '...'

export default defineComponent({
    props: ['firstname', 'lastname', ...usePerson.props],
    emits: usePerson.emits,
    setup(props, { emit }) {
        const person = usePerson()

        return {

        }
    }
})

The shape of the return value is essentially a flattened version of the mixins data, computed and methods properties, with data and computed being ref()'s. All other supported properties (lifecylces, watch) have nothing to expose externally.

const mixin = {
    data: () =>({
        a: 'A',
        b: 'B',
    }),
    computed: {
        c() { return this.A },
        d() { return this.B }
    },
    methods: {
        e() {
            return callSomething(this.a, this.c)
        }
    }
}

const useComposable = createComposableFromMixin(mixin)

would be turned into:

const {
    a, // ref('A')
    b, // ref('B')
    c, // computed ref 
    d, // computed ref
    e, // normal function
} = useComposable()

• Support Mixins that implicitly depend on properties/APIs from other mixins.
• Support Nested Mixins.
• Exclude specific properties from composables return value (essentially making some mixin properties private in the composable).

Out of scope / not planned

• mixins with implicit circular dependencies on one another.

creating a watcher imperatively in created will likely not work as expected, because in the created composable, that hooks is run before setup() returns, so any data properties declared in the mixin/composable will be missing on this.

Possible workarounds:

• use the normal watch:option
• create the watcher in beforeMount.

Typescript support is still considered unstable as we plan on improving the types, possibly introduction breaking changes to the types.

Caveats:

• For Type inference to work, each mixin object must have a props key. If your mixin does not include any props, set it to an empty object.
• props always need to be defined in object style. array style is currently not supported and will break type inference.
• the emits option cannot be provided in its array form, it must take the more verbose object form.

const mixin = defineMixin({
    props: {} // needed for proper tyep inference for now,
    emits: {
        'update:modelValue': (v?: any) => true, // this validator can be a NOOP returning `true`
    },
    data: () => ({
        // ...
    })
})

const composable = createCopmposableFromMixin(mixin)

This function does not do anything at runtime, it's just providing tpe inferrence for your mixins:

const mixin = {
    data: () => ({
        msg: 'Hello World',
    }),
    methods: {
        test() {
            this.msg // not inferreed correctly
        }
    }
}

// better:
import { defineMixin } from 'vue-mixable'
const mixin = defineMixin({
    props: {}, // needed, see caveat explained further up.
    data: () => ({
        msg: 'Hello World',
    }),
    methods: {
        test() {
            this.msg // properly inferred.
        }
    }
}

This function will offer full type inference for any mixin passed to it.

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