自动暴露子组件的方法，注意在TS下，需要自己声明类型，我这里全用any代替了

<template>
  <el-button @click="getFocus">获得焦点</el-button>
  <com ref="comRef" />
</template>

<script setup lang="ts">
import { ref } from 'vue'
import com from './components/com.vue'

const comRef = ref(null);
const getFocus = () => {
  (comRef.value! as any).focus()
};
</script>

子组件

<template>
  <el-input v-model="val" placeholder="请输入文本框" ref="inputRef" />
</template>

<script setup lang="ts">
import { ref } from 'vue'
import { InputInstance } from 'element-plus'

const val = ref('');
const inputRef = ref<null | InputInstance>(null);

defineExpose(new Proxy({}, {
  get(_target, key) {
    return (inputRef.value as any)?.[key];
  },
  has(_target, key) {
    return key in inputRef.value! as any;
  },
}))
</script>