Javascript - useTemplateRef is not reactive for arrays?

winwin
September 29, 2024
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0 votes
2 Answers

I’d like to react to changes made to an array of template ref elements created with a v-for loop over some collection of arbitrary objects. I’d like to pass this array to a component / composable and have it react to the changes.

The docs provide a way to save these elements to an array: https://vuejs.org/guide/essentials/template-refs.html#refs-inside-v-for

I’ve modified the provided example to see, if the resulting itemsRef array would be reactive. The code is:

<script setup>
import { ref, useTemplateRef, watch, markRaw } from 'vue'

const list = ref([1, 2, 3])

const itemRefs = useTemplateRef('items')

watch(itemRefs, () => {
  console.log("itemsRef:", itemRefs.value.length);
}, {deep: true});

watch(list, () => {
  console.log("list:", list.value.length, itemRefs.value.length);
}, { deep: true });
</script>

<template>
  <button @click="list.push(list.length + 1)">add</button>
  <ul>
    <li v-for="item in list" ref="items">
      {{ item }}
    </li>
  </ul>
</template>

But the return value of useTemplateRef seems to be a ShallowRef, judging from its TypeScript signature:

function useTemplateRef<T>(key: string): Readonly<ShallowRef<T | null>>

So the watch on itemRefs really runs just once:

As you can see, array’s contents are changing (list is updated), but the changes to itemRefs are not captured by vue. I tried making the watch deep, but it does not help.

Is there a way to make the ref not shallow somehow? Or maybe there is another way?

const { createApp, ref, useTemplateRef, watch, markRaw } = Vue;

const app = createApp({
  setup() {
    const list = ref([1, 2, 3]);

    const itemRefs = useTemplateRef('items');

    watch(itemRefs, () => {
      console.log("itemsRef: ", itemRefs.value.length);
    }, { deep: true });

    watch(list, () => {
      console.log("list: ", list.value.length, itemRefs.value.length);
    }, { deep: true });
    
    return { list }
  }
});

app.mount('#app');

<script src="https://unpkg.com/vue@3/dist/vue.global.prod.js"></script>

<div id="app">
  <button @click="list.push(list.length + 1)">add</button>
  <ul>
    <li v-for="item in list" ref="items">
      {{ item }}
    </li>
  </ul>
</div>

Answers

Chosen as BEST ANSWER

Using const elements = ref([]) with ref="elements" inside a v-for does not guarantee order, as per vue's docs.

Also, if your ref="elements" is a Component, the elements array will be full of ComponentPublicInstance elements.

To battle this, I used this gist as the base and created this composable:

export const useTemplateRefs = (elements: Ref<HTMLElement[]>) => {
  onBeforeUpdate(() => {
    elements.value = [];
  });
  const setElement = (elem: Element | ComponentPublicInstance | null, index: number): void => {
    if (elem == null) {
      return;
    }
    if (elem instanceof Element) {
      if (elem instanceof HTMLElement) {
        elements.value[index] = elem;
        return;
      }
    } else if (elem.$el instanceof HTMLElement) {
      elements.value[index] = elem.$el;
      return;
    }
    throw new Error("Unexpected element type");
  };
  return setElement;
};

Which can be used this way:

<script setup lang="ts">
const messages = ref([{id: 1, text: "Message"}]);
const messageRefs = ref<HTMLElement[]>([]);
const setRef = useTemplateRefs(messageRefs);
</script>

<template>
  <div class="container">
  <div
      v-for="(message, index) in messages"
      :key="message.id"
      :ref="el => setRef(el, index)"
    >
      {{ message.text }}
    </div>
  </div>
</template>

Now the messageRefs array is fully reactive and is in full sync with messages array.

(Edit)

itemRefs is updated (e.g reactive). But it’s always updated 1 render cycle after list has changed.

Wrap your console.log in nextTick (imported from ‘vue’) and the numbers will match:

const { createApp, ref, useTemplateRef, watch, nextTick } = Vue

const app = createApp({
  setup() {
    const list = ref([1, 2, 3])
    const itemRefs = useTemplateRef('items')
    watch(
      itemRefs,
      () => {
        console.log('itemsRef: ', itemRefs.value.length)
      },
      { deep: true }
    )
    watch(
      list,
      () => {
        nextTick(() =>
          console.log('list: ', list.value.length, itemRefs.value.length)
        )
      },
      { deep: true }
    )
    return { list }
  }
})

app.mount('#app')

<script src="https://unpkg.com/vue@3/dist/vue.global.prod.js"></script>

<div id="app">
  <button @click="list.push(list.length + 1)">add</button>
  <ul>
    <li v-for="item in list" ref="items">
      {{ item }}
    </li>
  </ul>
</div>

Also note you can’t watch it deeply, since it’s a shallow ref. To be able to get this functionality, use a normal ref:

const { createApp, ref, watch, nextTick } = Vue

const app = createApp({
  setup() {
    const list = ref([1, 2, 3])
    const items = ref([])
    watch(
      items,
      () => {
        console.log('itemsRef: ', items.value.length)
      },
      { deep: true }
    )
    watch(
      list,
      () => {
        nextTick(() =>
          console.log('list: ', list.value.length, items.value.length)
        )
      },
      { deep: true }
    )
    return { list, items }
  }
})

app.mount('#app')

<script src="https://unpkg.com/vue@3/dist/vue.global.prod.js"></script>

<div id="app">
  <button @click="list.push(list.length + 1)">add</button>
  <ul>
    <li v-for="item in list" ref="items">
      {{ item }}
    </li>
  </ul>
</div>

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Javascript – useTemplateRef is not reactive for arrays?

Answers