Vue 3 how to get information about $children

Question

This my old code with VUE 2 in Tabs component:

created() {
   this.tabs = this.$children;
}

Tabs:

<Tabs> 
  <Tab title="tab title">
    ....
  </Tab>
  <Tab title="tab title">
    ....
  </Tab> 
</Tabs>

VUE 3: How can I get some information about childrens in Tabs component, using composition API? Get length, iterate over them, and create tabs header, ...etc? Any ideas? (using composition API)

Answer 1

This is my Vue 3 component now. I used provide to get information in child Tab component.

<template>
  <div class="tabs">
    <div class="tabs-header">
      <div
        v-for="(tab, index) in tabs"
        :key="index"
        @click="selectTab(index)"
        :class="{'tab-selected': index === selectedIndex}"
        class="tab"
      >
        {{ tab.props.title }}
      </div>
    </div>
    <slot></slot>
  </div>
</template>

<script lang="ts">
import {defineComponent, reactive, provide, onMounted, onBeforeMount, toRefs, VNode} from "vue";
    
interface TabProps {
  title: string;
}
    
export default defineComponent({
  name: "Tabs",
  setup(_, {slots}) {
    const state = reactive({
      selectedIndex: 0,
      tabs: [] as VNode<TabProps>[],
      count: 0
    });
    
    provide("TabsProvider", state);
    
    const selectTab = (i: number) => {
      state.selectedIndex = i;
    };
    
    onBeforeMount(() => {
      if (slots.default) {
        state.tabs = slots.default().filter((child) => child.type.name === "Tab");
      }
    });

    onMounted(() => {
      selectTab(0);
    });

    return {...toRefs(state), selectTab};
  }
});
</script>

Tab component:

<script lang="ts">
export default defineComponent({
  name: "Tab",
  setup() {
    const index = ref(0);
    const isActive = ref(false);

    const tabs = inject("TabsProvider");

    watch(
      () => tabs.selectedIndex,
      () => {
        isActive.value = index.value === tabs.selectedIndex;
      }
    );

    onBeforeMount(() => {
      index.value = tabs.count;
      tabs.count++;
      isActive.value = index.value === tabs.selectedIndex;
    });
    return {index, isActive};
  }
});
</script>

<template>
  <div class="tab" v-show="isActive">
      <slot></slot>
  </div>
</template>

Answer 2

Oh guys, I solved it:

this.$slots.default().filter(child => child.type.name === 'Tab')

Answer 3

If you copy pasted same code as me

then just add to the "tab" component a created method which adds itself to the tabs array of its parent

created() {
    
        this.$parent.tabs.push(this); 

    },

Answer 4

Based on the answer of @Urkle:

/**
 * walks a node down
 * @param vnode
 * @param cb
 */
export function walk(vnode, cb) {
    if (!vnode) return;

    if (vnode.component) {
        const proxy = vnode.component.proxy;
        if (proxy) cb(vnode.component.proxy);
        walk(vnode.component.subTree, cb);
    } else if (vnode.shapeFlag & 16) {
        const vnodes = vnode.children;
        for (let i = 0; i < vnodes.length; i++) {
            walk(vnodes[i], cb);
        }
    }
}

In addition to the accepted answer:

Instead of

this.$root.$children.forEach(component => {})

write

walk(this.$root, component => {})

And this is how i got it working for me.

Answer 5

I found this updated Vue3 tutorial Building a Reusable Tabs Component with Vue Slots very helpful with explanations that connected with me.

It uses ref, provide and inject to replace this.tabs = this.$children; with which I was having the same problem.

I had been following the earlier version of the tutorial for building a tabs component (Vue2) that I originally found Creating Your Own Reusable Vue Tabs Component.

Answer 6

I had the same problem, and after doing so much research and asking myself why they had removed $children, I discovered that they created a better and more elegant alternative.

It's about Dynamic Components. (<component: is =" currentTabComponent "> </component>).

The information I found here:

https://v3.vuejs.org/guide/component-basics.html#dynamic-components

I hope this is useful for you, greetings to all !!

Answer 7

A per Vue documentation, supposing you have a default slot under Tabs component, you could have access to the slot´s children directly in the template like so:

// Tabs component

<template>
  <div v-if="$slots && $slots.default && $slots.default()[0]" class="tabs-container">
    <button
      v-for="(tab, index) in getTabs($slots.default()[0].children)"
      :key="index"
      :class="{ active: modelValue === index }"
      @click="$emit('update:model-value', index)"
    >
      <span>
        {{ tab.props.title }}
      </span>
    </button>
  </div>
  <slot></slot>
</template>

<script setup>
  defineProps({ modelValue: Number })

  defineEmits(['update:model-value'])

  const getTabs = tabs => {
    if (Array.isArray(tabs)) {
      return tabs.filter(tab => tab.type.name === 'Tab')
    } else {
      return []
    }
</script>

<style>
...
</style>

And the Tab component could be something like:

// Tab component

<template>
  <div v-show="active">
    <slot></slot>
  </div>
</template>

<script>
  export default { name: 'Tab' }
</script>

<script setup>
  defineProps({
    active: Boolean,
    title: String
  })
</script>

The implementation should look similar to the following (considering an array of objects, one for each section, with a title and a component):

...
<tabs v-model="active">
  <tab
    v-for="(section, index) in sections"
    :key="index"
    :title="section.title"
    :active="index === active"
  >
    <component
      :is="section.component"
    ></component>
  </app-tab>
</app-tabs>
...
<script setup>
import { ref } from 'vue'

const active = ref(0)
</script>

Another way is to make use of useSlots as explained in Vue´s documentation (link above).

Answer 8

In 3.x, the $children property is removed and no longer supported. Instead, if you need to access a child component instance, they recommend using $refs. as a array

https://v3-migration.vuejs.org/breaking-changes/children.html#_2-x-syntax

Answer 9

With script setup syntax, you can use useSlots: https://vuejs.org/api/sfc-script-setup.html#useslots-useattrs

<script setup>
import { useSlots, ref, computed } from 'vue';

const props = defineProps({
    perPage: {
        type: Number,
        required: true,
    },
});

const slots = useSlots();

const amountToShow = ref(props.perPage);
const totalChildrenCount = computed(() => slots.default()[0].children.length);
const childrenToShow = computed(() => slots.default()[0].children.slice(0, amountToShow.value));
</script>

<template>
    <component
        :is="child"
        v-for="(child, index) in childrenToShow"
        :key="`show-more-${child.key}-${index}`"
    ></component>
</template>

Answer 10

My solution for scanning children elements (after much sifting through vue code) is this.

export function findChildren(parent, matcher) {
  const found = [];
  const root = parent.$.subTree;
  walk(root, child => {
    if (!matcher || matcher.test(child.$options.name)) {
      found.push(child);
    }
  });
  return found;
}

function walk(vnode, cb) {
  if (!vnode) return;

  if (vnode.component) {
    const proxy = vnode.component.proxy;
    if (proxy) cb(vnode.component.proxy);
    walk(vnode.component.subTree, cb);
  } else if (vnode.shapeFlag & 16) {
    const vnodes = vnode.children;
    for (let i = 0; i < vnodes.length; i++) {
      walk(vnodes[i], cb);
    }
  }
}

This will return the child Components. My use for this is I have some generic dialog handling code that searches for child form element components to consult their validity state.

const found = findChildren(this, /^(OSelect|OInput|OInputitems)$/);
const invalid = found.filter(input => !input.checkHtml5Validity());

Answer 11

In 3.x version, the $children is removed and no longer supported. Using ref to access children instance.

<script setup>
import { ref, onMounted } from 'vue'
import ChildComponent from './ChildComponent .vue'

const child = ref(null)

onMounted(() => {
   console.log(child.value) // log an instance of <Child />
})
</script>

<template>
  <ChildComponent ref="child" />
</template>

Detail: https://vuejs.org/guide/essentials/template-refs.html#template-refs

Answer 12

To someone wanting whole code:

Tabs.vue

<template>
    <div>
        <div class="tabs">
            <ul>
                <li v-for="tab in tabs" :class="{ 'is-active': tab.isActive }">
                    <a :href="tab.href" @click="selectTab(tab)">{{ tab.name }}</a>
                </li>
            </ul>
        </div>

        <div class="tabs-details">
            <slot></slot>
        </div>
    </div>
</template>

<script>
    export default {
        name: "Tabs",
        data() {
            return {tabs: [] };
        },
        created() {

        },
        methods: {
            selectTab(selectedTab) {
                this.tabs.forEach(tab => {
                    tab.isActive = (tab.name == selectedTab.name);
                });
            }
        }
    }
</script>

<style scoped>

</style>

Tab.vue

<template>
    <div v-show="isActive"><slot></slot></div>
</template>

<script>
    export default {
        name: "Tab",
        props: {
            name: { required: true },
            selected: { default: false}
        },

        data() {

            return {
                isActive: false
            };

        },

        computed: {

            href() {
                return '#' + this.name.toLowerCase().replace(/ /g, '-');
            }
        },

        mounted() {

            this.isActive = this.selected;

        },

        created() {

            this.$parent.tabs.push(this);

        },
    }
</script>

<style scoped>

</style>

App.js

<template>
    <Tabs>
                    <Tab :selected="true"
                         :name="'a'">
                        aa
                    </Tab>
                    <Tab :name="'b'">
                        bb
                    </Tab>
                    <Tab :name="'c'">
                        cc
                    </Tab>
                </Tabs>
<template/>

Answer 13

I made a small improvement to Ingrid Oberbüchler's component as it was not working with hot-reload/dynamic tabs.

in Tab.vue:

onBeforeMount(() => {
  // ...
})
onBeforeUnmount(() => {
  tabs.count--
})

In Tabs.vue:

const selectTab = // ...
// ...
watch(
  () => state.count,
  () => {
    if (slots.default) {
      state.tabs = slots.default().filter((child) => child.type.name === "Tab")
    }
  }
)