Elementui按钮设置默认选中状态的实现过程

<el-row>
 <el-button>默认按钮</el-button>
 <el-button type="primary">主要按钮</el-button>
 <el-button type="success">成功按钮</el-button>
 <el-button type="info">信息按钮</el-button>
 <el-button type="warning">警告按钮</el-button>
 <el-button type="danger">危险按钮</el-button>
</el-row>

<el-row>
 <el-button plain>朴素按钮</el-button>
 <el-button type="primary" plain>主要按钮</el-button>
 <el-button type="success" plain>成功按钮</el-button>
 <el-button type="info" plain>信息按钮</el-button>
 <el-button type="warning" plain>警告按钮</el-button>
 <el-button type="danger" plain>危险按钮</el-button>
</el-row>

<el-button type="danger"  plain>是朴素按钮</el-button>
<el-button type="danger" :plain="false">非朴素按钮</el-button>

<template>
 ...
    <div class="row">
     	<el-button type="danger" :plain="selectA" @click="clickA">默认选中按钮</el-button>
		<el-button type="danger" :plain="selectB" @click="clickB">按钮</el-button>
    </div>
  ...
</template>
<script>
export default {
 	...
  	data: function () {
		return {
			selectA: false,
			selectB: true,
			}
		}
	...
	methods: {
	 // 默认选中按钮事件
		clickA() {
			this.selectA = false;
			this.selectB = true;
		},
		// 按钮事件
		clickB() {
			this.selectA = true;
			this.selectB = false;
		},
	}
	...
</script>