Description
What problem does this feature solve?
When using the babel-preset-app's polyfills option, the default polyfills are replaced.
I just wanted to include es6.array.find-index using the polyfills option. Suddenly, all the Promise.finally in my source code didn't work anymore in IE11. es6.promise was included properly because of useBuiltIns: 'usage', but es7.promise.finally was not included. Even adding es7.promise.finally to the polyfills option didn't work as expected. I think es6.promise, which is included via usage after the es7.promise.finally pre-include, overrides it. Therefore I had to prepend also es6.promise to the polyfills option.
If you know how the pre-includes and useBuiltIns work, it's probably not a big deal - otherwise it can be tricky.
What does the proposed API look like?
A preset option to extend the default polyfills, instead of replacing them, so we don't have to check the docs to copy/paste the default polyfills.
or
Update the docs, mentioning that the default polyfills are replaced and you likely want to include all the default polyfills first before adding another one.