The re-expressed title is: v-if based on DOM updates

Question

I have some elements rendered using v-for Each element contains text and buttons I need to show the button only when the text overflows the height of the div

<div v-for="el in elements" :key="el.id">
    <span>{{ el.text }}</span>
    <button>Click me</button>
</div>

The obvious solution is to use v-if, but on what basis should I base my judgment? I need to calculate the height of the text and decide whether to show the button or not Therefore, I need to use refs to reference the divs and a function to determine whether to display:

<template>
    <button @click="addDiv"> 点击添加div </button>
    <div v-for="(el, index) in elements" :key="el.id">
        <span ref="items">{{ el.text }}</span>
        <button v-if="showButton(index)">Click me</button>
    </div>
</template>

<script setup lang="ts">
//imports
const elements = ref([]);
const addDiv = function() { 
    elements.value.push({ text: "测试", id: Date.now() })
}
const items = ref();
const showButton = function (index) {
    const item = items.value[index] as HTMLElement;
    return item.scrollHeight > item.offsetHeight
}
</script>

But I found that the problem is that items is out of sync with the DOM. So obviously, the DOM is updated asynchronously and that's why my data is a bit late So I decided to add nextTick() in my showButton function, but it started returning Promise which caused the v-if to always be true

<template>
    <button @click="addDiv"> 点击添加div </button>
    <div v-for="(el, index) in elements" :key="el.id">
        <span ref="items">{{ el.text }}</span>
        <button v-if="showButton(index)">Click me</button>
    </div>
</template>

<script setup lang="ts">
//imports
const elements = ref([]);
const addDiv = function() { 
    elements.value.push({ text: "测试", id: Date.now() })
}
const items = ref();
const showButton = function (index) {
    nextTick(() => {
        const item = items.value[index] as HTMLElement;
        return item.scrollHeight > item.offsetHeight
    })
}
</script>

So is there a way to show or hide my buttons specifically for each element?

Answer 1

I used watchers in Vue to complete this operation. I hope it can be helpful to you!

<template>
  <button @click="addDiv">点击添加div</button>
  <div
    v-for="el in elements"
    :key="el.id"
  >
    <span ref="items">{{ el.text }}</span>
    <button v-if="el.showButton">点击我</button>
  </div>
</template>

And the script part, I have updated the input part:

<script setup lang="ts">
  //imports
  import { ref, watch } from 'vue';

  const elements = ref<Array<any>>([]);
  const items = ref<Array<HTMLElement>>([]);

  const addDiv = function () {
    elements.value.push({ text: '测试', id: Date.now(), showButton: false });
  };

  watch(items.value, (newItems) => {
    console.log('items changed');
    let cpt = 0;

    // you can do it with a for loop too
    newItems.forEach((item) => {
      if (item.scrollHeight > item.offsetHeight) {
        console.log('overflow -> show button');
        elements.value[cpt].showButton = true;
      }
      cpt++;
    });
  });
</script>