安装vue element-ui时报错。

deprecated core-js@2.6.12: core-js@<3 is no longer maintained and not recommended for usage due to the number of issues. Please, upgrade your dependencies to the actual version of core-js@3.

不推荐使用的core-js@2.6.12：由于问题的数量，不再维护core-js @ <3，因此不建议使用它。 请将您的依赖项升级到core-js @ 3的实际版本。

解决方法：

因为vue cli 升级至v4后，将内部的core-js依赖升级到v3，

所以需要我们给core-js做一个升级 npm install -g core-js@3.1.1也可以npm i core-js（v3以上的都行，目前发布到3.6.5），

或者改一下 nuxt.config.js 中的配置 。

为什么升级呢？因为vue cli中nuxt.js默认依赖的是core-js 2

可是执行后 还是报错

PS C:\Users\andyf\vue\andyvue> npm install -g core-js@3.1.1
npm WARN deprecated core-js@3.1.1: core-js@<3.3 is no longer maintained and 
not recommended for usage due to the number of issues. Because of the V8 engine whims, 
feature detection in old core-js versions could cause a slowdown up to 100x even if nothing is polyfilled. 
Please, upgrade your dependencies to the actual version of core-js.

> core-js@3.1.1 postinstall C:\Users\andyf\AppData\Roaming\npm\node_modules\core-js
> node scripts/postinstall

Thank you for using core-js ( https://github.com/zloirock/core-js )!

Please consider supporting of core-js on Open Collective or Patreon: 
> https://opencollective.com/core-js 
> https://www.patreon.com/zloirock 

Also, the author of core-js ( https://github.com/zloirock ) is looking for a good job -)

npm WARN deprecated core-js@3.1.1: core-js@<3.3 is no longer maintained and not recommended for usage due to the number of issues. Because of the V8 engine whims, feature detection in old core-js versions could cause a slowdown up to 100x even if nothing is polyfilled. Please, upgrade your dependencies to the actual version of core-js.

npmWARN不推荐使用core-js@3.1.1：由于问题的数量，不再维护core-js @ <3.3，不建议使用它。 由于V8引擎的异想天开，即使没有填充任何东西，旧版core-js版本中的功能检测也可能导致速度降低多达100倍。 请将您的依赖项升级到core-js的实际版本。

最后我的解决方法是直接在vue ui 中添加插件。