Add core-js implementation

[zloirock]

No description provided.

[ljharb]

It is very irresponsible to publish this as a polyfill; it’s not even stage 2 yet, and the name “unThis” will never achieve consensus.

[zloirock]

It's unlogical to write it each time when I add a polyfill for an early-stage proposal. Please, avoid it next time. It's only for experimentation and changing name in the future is additional protection from possible problems.

[ljharb]

I didn't write it each time; you made similar PRs on two other pre-stage-3 proposals. This one, however, is particularly dangerous, and I think it would be quite harmful to link to it from the proposal's readme.

"Only for experimentation" is irrelevant; modifying builtins in nonstandard ways harms the web, for whatever purpose.

[zloirock]

Maybe not each time, but you write it too often. I have more experience in polyfills and web stability than you, so please don't say me what should I do and what I should not do.

"Only for experimentation" is irrelevant

This is an unfounded statement. Without pre-stage 3 polyfills you cant touch the new functionality and check how it works in real life, with other new features. Without it, too many proposals could have the required feedback too late.

harms the web

Some of your cases like this make much more harm for the web than current.

[ljharb]

It's not an unfounded statement. Prior to stage 3, all sorts of experimentation can be done without needing to install anything into the environment, and is often done.

The TC39 process doesn't want that feedback until stage 3 - that is what that stage is for.

[zloirock]

Stage 3 presupposes feedback from JS engine implementors and mass users. As you could see in the process document, polyfills are expected on stage-1 and they help for further advance.

[ljharb]

Thanks; I'll update the process document so it no longer incorrectly indicates this about polyfills.

[js-choi]

Thank you for your work on this, @zloirock. However, in this particular case, I would like to avoid people from using any public polyfills for now, because this proposal is currently very unstable. In particular, its very name, “un-this”, is unstable and likely to change (#1).

We can open this pull request back up once the proposal settles more. Thank you again for your work.

[zloirock]

@js-choi, since it's only for experiments, instability of the name is not a big problem, however ok, let's wait for stabilization -)