Promise.prototype.finally() broken in Firefox

Version

3.0.0-rc.10

Node and OS info

Node 10.6.0 / Yarn 1.9.2 / macOS 10.13.5

Steps to reproduce

1. Clone https://github.com/mserajnik/vue-cli-promise-finally
2. Install with Yarn
3. Run with yarn serve
4. Open the development URL in Firefox (tested under Firefox 61.0.1)
5. Check the console: [Vue warn]: Error in created hook: "TypeError: this.fetchData(...).then(...).catch(...).finally is not a function"

What is expected?

According to the MDN web docs, Promise.prototype.finally() is supported natively in Firefox since 58, so it should work, even without any polyfill.

What is actually happening?

Promise.prototype.finally() does not work in Firefox (61.0.1).

---

Not sure if I’m missing something obvious here – I’m not even sure if this is actually a bug or just a configuration issue (maybe I have to adjust my babel.config.js in some way?). What is weird is that Promise.prototype.finally() works in Safari when I run the same test app, which doesn’t have native support for it apparently – so the polyfill seems to be working there. I can only reproduce the issue in Firefox. A friend has also confirmed the same issue in Firefox under Windows 10.

Oh, and sorry if this issue belongs somewhere else. Since I couldn’t pin down if it’s a Firefox bug, an issue with Babel or one with the @vue/app preset (or just a configuration error on my end), it made the most sense to me to open it here first.

[yyx990803]

This is an issue in core-js - its promise polyfill replaces the native Promise in Firefox, however according to author of core-js, it is doing it because Firefox’s Promise implementation somehow fails a subclassing check so is technically not spec-compliant.

For now I’ve included es7.promise.finally by default to fix this in Vue CLI.

[imtbl]

Doing the following seems to work:

// babel.config.js

module.exports = {
  presets: [
    ['@vue/app', { useBuiltIns: 'entry' }]
  ]
}

// src/main.js

import '@babel/polyfill'

[…]

It does increase the bundle size a bit (as expected), but that’s not really an issue.

According to this comment from Brian Ng:

Yep, there’s currently no usage mapping for .then, .catch or .finally.

So, issue solved for me. Do you think you could mention this limitation of having useBuiltIns in usage mode somewhere in the readme of @vue/babel-preset-app? I know that’s an issue/limitation with @babel/preset-env itself, but given that @vue/cli is pretty much zero config by default and very beginner-friendly for people who haven’t worked with webpack/Babel/etc. before, this is likely one of the first places they’d look if they encountered such an issue.