Fix babel useBuiltIns core-js warning

• I confirm that this is an issue rather than a question.

Bug report

When running ‘vanilla’ build see the following warning in the console

WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.


You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:

  npm install --save core-js@2    npm install --save core-js@3
  yarn add core-js@2              yarn add core-js@3

Version

@vuepress/core@1.0.0-alpha.44

Steps to reproduce

$ mkdir test; cd test; npm init # accept defaults $ npm install vuepress@next $ echo ‘# Hello VuePress’ > README.md $ ./node_modules/.bin/vuepress build

What is expected?

no warnings about useBuiltIns

What is actually happening?

scary warning 😉

actually, some additional information on how I stumbled across this. In my case adding nuxt@2.5.0 (used core-js 3) caused the “vupress build” to fail. Whereas adding nuxt@2.5.1 (uses core-js 2) makes the vuepress build error and warning go away. Related to https://github.com/nuxt/nuxt.js/issues/5313

Other relevant information

• Your OS: Windows 10
• Node.js version: 8.15.1
• Browser version: n/a
• Is this a global or local install? local
• Which package manager did you use for the install? npm 6.4.1
• Does this issue occur when all plugins are disabled? unsure, only using defaults

[sidwaseem]

Adding "corejs": "3.0.0" in the .babelrc file turned off the warnings.

"presets": [
        [
            "@babel/preset-env",
            {
                "useBuiltIns": "usage", // "usage" | "entry" | false, defaults to false.
                "corejs": "3.0.0",
                "targets": {
                    "esmodules": true,
                    "ie": "11"
                }
            }
        ]
    ],

[ghenry]

I see this on the latest vue cli and vue js SPA build too.