Use babel transform runtime over babel polyfill

[evan-10e]

Problem

Projects that depend on babel-polyfill and fetch-mock will crash with the following error.

Solution

In short: Libraries should not be using babel-polyfill, but rather babel transform runtime.

Additional Context

Babel team members warn that if you are writing a library - babel polyfill should not be used because it can pollute the globals used by project owners.

If you are writing a library, you should not be using babel-polyfill. Having a library mutate the global state of the browser environment is not a good idea. If you need a standalone library you should be using babel-runtime via transform-runtime, or if you don't want to do that, you should make it a requirement that uses of your library load a polyfill first, and your code should assume it is there.

Logan Smyth (member and contributor of babel) babel/babel#4019 (comment)

As such, Fetch-mock's improper use of babel is causing projects to crash in this fashion. babel/babel#4019 (comment)

[wzph-10e]

+1

[wheresrhys]

Hi. Sorry for the slow response. Not had much time to maintain the library lately.

I agree with your appraisal, but don't think I can release this as a patch - babel polyfilling has been a discussion point in issues before, and I think this will break lots of people's tests. I don't want to deal with the fallout from that.

So I think this should be released as v8 of the library. Please could you search the repo (mainly docs) for mentions of v7 and update to say v7/8 https://github.com/wheresrhys/fetch-mock/search?q=v7&unscoped_q=v7. I will add a changelog note once released to explain what the difference between v7 and 8 is.

[ndelangen]

Could this be combined with an upgrade to core-js v3?

Or would this remove the need for core-js entirely?

Some users of storybook are hitting the core-js 3 incompatibility with this lib:
storybookjs/storybook#7445

I would be open to helping resolve this, Are you still working on this @evan-10e @wheresrhys ?

[evan-10e]

@ndelangen I discovered that my bundle script was duplicated in the page head. Removing the dup solved the issue for me.

[wheresrhys]

v8.0.0-alpha.2 attempts to address this issue. Please leave a 👍 on the pull request #457 if your problem is solved, or alternatively leave a comment @evan-10e @ndelangen @wzph-10e