vant组件cdn引入和直接按需引入，导致的问题

cdn引入需要使用完整闭合标签

<van-overlay :show="loading">
   <van-loading type="spinner" size="40px"></van-loading>
</van-overlay>

main.js

按需引入配置

module.exports = {  
    presets: [    
        '@vue/cli-plugin-babel/preset'  
    ],  
    plugins: [    
        [
            "@babel/plugin-transform-runtime", 
            {      
                corejs: 3    
            }
        ],    
        ["import",      
            {        
                libraryName: "vant",        
                libraryDirectory: "es",        
                style: true      
            }    
        ]  
   ]
}

使用自闭合标签
<van-overlay :show="loading">
   <van-loading type="spinner" size="40px" />
</van-overlay>