feat: add support for observing selected carousel slide index

[itspolly]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This change adds a new event emitter to the Carousel component that emits the index of the currently selected slide. This change is required to make carousels support reactivity: i.e, passing state from one carousel to another.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[itspolly]

I tried to achieve this functionality without this change by adding event listeners to the emblaApi prop (i used a reference to access an instance of the Carousel component in the setup script) but that didn't work.

[pkg-pr-new]

npm i https://pkg.pr.new/@nuxt/ui@3678

commit: 3b8f9c8

[itspolly]

Here's the code that I was using to try and achieve this functionality via the emblaApi prop:

<style>
@import "tailwindcss";
@import "@nuxt/ui";
@import "assets/css/main.css";
</style>

<script setup lang="ts">
const runtimeConfig = useRuntimeConfig();
const carousel = useTemplateRef("carousel");

const props = defineProps<{
  item: any,
  selectedImageIndex: number
}>();

const emit = defineEmits<{ 
  close: [],
  selectedSlideIndexUpdated: [number]
}>();

// function selectedSlideIndexUpdated(slide: number) {
//   emit('selectedSlideIndexUpdated', slide);
// }

onMounted(() => {
  const emblaApi = carousel.value?.emblaApi;

  function selectedSlideIndexUpdated() {
    console.log("selected slide changed");

    const slide = emblaApi?.selectedScrollSnap();
    if (!slide) return;
    console.log('selected slide changed');
    emit('selectedSlideIndexUpdated', slide);
  }

  emblaApi?.on('init', selectedSlideIndexUpdated)
  emblaApi?.on('reInit', selectedSlideIndexUpdated)
  emblaApi?.on('select', selectedSlideIndexUpdated)
});
</script>

<template>
    <UModal
      :close="{ onClick: () => emit('close') }"
      :title="item.name"
      :description="item.description"
      :ui="{ title: 'font-semibold text-xl', description: 'font-normal' }"
    >
        <template #body>
          <!-- @select="selectedSlideIndexUpdated" -->
          <UCarousel ref="carousel" :start-index="selectedImageIndex" v-slot="{ item: imageKey }" :items="item.imageNames" :ui="{ item: 'basis-full' }" class="rounded-lg overflow-hidden" arrows>
            <img :src="`${runtimeConfig.public.instance.prefix ?? ''}/items/img/${item.identifier}/${imageKey}`" class="w-full" draggable="true">
          </UCarousel>
        </template>
    </UModal>
</template>

note that selected slide changed is never logged.

This issue is caused because the embla EventHandler implementation only supports one callback per event type and the handlers that nuxt ui registers overwrites any handlers that my script adds.

[benjamincanac]

Suggested change

	const emit = defineEmits<{
	select: [selectedIndex: number]
	}>()
	const emits = defineEmits<CarouselEmits>()

[benjamincanac]

Suggested change

	emit('select', selectedIndex.value)
	emits('select', selectedIndex.value)