代码

demo\src\App.vue
    <script setup>
        import { ref,reactive } from 'vue'
        
        const selected = ref('2')
        const selected2 = ref('')
        const selected3 = ref('C')
        const selected4 = ref(['1','3'])

        const data = reactive({
            options: [
                { value: 'A', label: '前端', },
                { value: 'B', label: '后端', },
                { value: 'C', label: '服务端', }
            ]
        })

        //回调
        const selectChange = (val) => {
            console.log("selectChange:", val)
        }
    </script>

    <template>
        <div style="width: 300px;">
            <h3>下拉框</h3>
            <el-select v-model="selected" placeholder="请选择">
                <el-option value="1" label="前端" />
                <el-option value="2" label="后端" />
                <el-option value="3" label="服务端" />
            </el-select>

            <h3>下拉框 - 事件绑定</h3>
            <el-select v-model="selected2" @change="selectChange" placeholder="请选择">
                <el-option value="a" label="前端" />
                <el-option value="b" label="后端" />
                <el-option value="c" label="服务端" />
            </el-select>

            <h3>动态下拉框</h3>
            <el-select v-model="selected3" placeholder="请选择">
                <el-option v-for="item in data.options" 
                :value="item.value" 
                :label="item.label"
                :key="item.value" />
            </el-select>

            <h3>多选 - multiple</h3>
            <el-select v-model="selected4" multiple @change="selectChange" placeholder="请选择">
                <el-option value="1" label="前端" />
                <el-option value="2" label="后端" />
                <el-option value="3" label="服务端" />
            </el-select>
        </div>
    </template>

    <style scoped>

    </style>