Array methods `flat` and `flatMap` are not polyfilled

Version

3.6.3

Reproduction link

https://github.com/runarberg/vue-cli-minimal-example

Environment info

npx @vue/cli info

Environment Info:

  System:
    OS: Linux 4.15 Ubuntu 18.04.2 LTS (Bionic Beaver)
    CPU: (4) x64 Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz
  Binaries:
    Node: 11.2.0 - ~/.nvm/versions/node/v11.2.0/bin/node
    Yarn: Not Found
    npm: 6.4.1 - ~/.nvm/versions/node/v11.2.0/bin/npm
  Browsers:
    Chrome: Not Found
    Firefox: 66.0.2
  npmPackages:
    @vue/babel-helper-vue-jsx-merge-props:  1.0.0-beta.3 
    @vue/babel-plugin-transform-vue-jsx:  1.0.0-beta.3 
    @vue/babel-preset-app:  3.6.0 
    @vue/babel-preset-jsx:  1.0.0-beta.3 
    @vue/babel-sugar-functional-vue:  1.0.0-beta.3 
    @vue/babel-sugar-inject-h:  1.0.0-beta.3 
    @vue/babel-sugar-v-model:  1.0.0-beta.3 
    @vue/babel-sugar-v-on:  1.0.0-beta.3 
    @vue/cli-overlay:  3.6.0 
    @vue/cli-plugin-babel: ^3.6.0 => 3.6.0 
    @vue/cli-plugin-eslint: ^3.6.0 => 3.6.0 
    @vue/cli-service: ^3.6.0 => 3.6.0 
    @vue/cli-shared-utils:  3.6.0 
    @vue/component-compiler-utils:  2.6.0 
    @vue/preload-webpack-plugin:  1.1.0 
    @vue/web-component-wrapper:  1.2.0 
    eslint-plugin-vue: ^5.0.0 => 5.2.2 
    vue: ^2.6.10 => 2.6.10 
    vue-eslint-parser:  2.0.3 
    vue-hot-reload-api:  2.3.3 
    vue-loader:  15.7.0 
    vue-style-loader:  4.1.2 
    vue-template-compiler: ^2.5.21 => 2.6.10 
    vue-template-es2015-compiler:  1.9.1 
  npmGlobalPackages:
    @vue/cli: Not Found

Steps to reproduce

1. Create a new vue project with babel plugin
2. In your app use the flat or flatMap array methods

What is expected?

These array methods should be polyfilled

What is actually happening?

They are not polyfilled

---

• Open your app in Chrome, Firefox or Safari and see it working.
• Open it in Edge and see an error message:

[Vue warn]: Error in render: "TypeError: Object doesn't support property or method 'flat'"
TypeError: Object doesn't support property or method 'flat'

Note that babel is configured to polyfill any method that is used, this includes Array.from in the above example.

Also note that Array.prototype.{flat,flatMap} were approved for stage 4 in at TC-39 last January and have been moved to stable in core-js.

[gavvvr]

Just noticed my app can’t work in IE because of missing flatMap.

Adding

import “core-js/fn/array/flat-map”;

to main.js solved the problem for me

[sodatea]

1. It’s only stable in core-js 3, while we use core-js 2
2. https://github.com/babel/website/blob/master/docs/plugin-transform-runtime.md#core-js-aliasing

   Instance methods such as “foobar”.includes(“foo”) will only work when using corejs: 3.

Will be fixed once we upgraded to core-js v3 in Vue CLI v4.