我有一个输入字段，根据用户输入的字符数，该输入字段会自动替换为文本区域和相同的内容：

<input type="text" v-if="myString.length <= 20" v-model="myString"/></pre>
<p>我遇到的问题是，当用户输入第 21 个字符时焦点会丢失。因此，用户会感到恼火，因为当他键入第 22 个字符时，该字符没有出现在文本区域中（没有焦点）。
<strong>我怎样才能将焦点设置在新渲染的文本区域上？</strong>这里的问题是它会自动渲染。否则我可以在文本区域上设置一个引用并调用 focus()。</p>
<p>另一个问题是删除第 21 个字符以及从文本区域切换回输入元素。</p>            </div>
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                                <a href="/member/1271634.html" target="_blank" class="wdcdcName">P粉459440991<b class="wdxqRcT colorGrey">2024-03-31 20:04:17</b></a>
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                            <div class="wdcdcCons"><p>（复制我的评论，因为这可能会有所帮助）</p>
<p>用 <code>textarea</code> 替换 <code>input</code> 元素可能会产生糟糕的用户体验。为什么不从一开始就使用 <code>textarea</code> 呢？如果您希望样式根据输入长度而改变，例如如果超过 20 个字符，则增加高度，那么您可以使用 CSS 来做到这一点。</p>
<pre class="brush:html;toolbar:false;"><script setup>
const props = defineProps({
  modelValue: String,
})
</script><template><textarea :value="modelValue" :rows="1" :style="modelValue.length > 20 ? { minHeight: '100px' } : { minHeight: '0px' }">

演示（分叉来自@tony19）