先放效果：

 

 代码

<template><el-input v-model="num" placeholder="请输入数字" /><el-button type="primary" @click="changeNum">取绝对值</el-button>
</template>

import { ref } from "vue";const num = ref();
const changeNum = () => {if (num.value) {num.value = Math.abs(num.value);}
};