Allow alternative implementations of BigInt compatibility libraries

[12wrigja]

Currently, the polyfill makes heavy use of the big-integer library to polyfill native BigInt. It would be preferable if this support library could be wrapped behind an interface and alternative implementations could be used instead.

[ptomato]

Would it work for your purposes if the polyfill used native BigInt directly, or do you need to support environments that don't have it?

[12wrigja]

We will need to support IE11, so using BigInt directly won't work for us.

[12wrigja]

Pondering this more, this would also be an issue for usage of the Intl APIs, though without having looked over the implementation much maybe there's not a large variety of API surface needed from both, and so accessing those APIs indirectly wouldn't be too much of a hassle.

[ptomato]

JSBI might be an option, since that's already an interface that is designed to be transpiled into native BigInt operations when applicable. We looked at it last year but decided not to adopt it due to already having big-integer, but maybe now this is a good reason to proceed with it?

[12wrigja]

I've spoken with the JSBI maintainers and they are onboard to review a migration of the JSBI source to TypeScript, which I'm undertaking now.

JSBI is designed to be transpiled to native BigInt calls via a Babel plugin which sounds good for code-size assuming that this isn't already happening for big-integer.

[12wrigja]

Though I'd prefer to see GoogleChromeLabs/jsbi#22 resolved and use JSBI as if it exported top-level functions. It's unclear to me at the moment whether that change is something that can be done in a backwards-incompatible way and work correctly with the rewriting plugin.

[ptomato]

(the big-integer calls are definitely not being transpiled, they are wrappers around the native BigInt calls, so this would be a good improvement)

[Pyrolistical]

Shouldn't we go the other way? Have the source implemented with native BigInt and direct people to https://github.com/Yaffle/babel-plugin-transform-bigint if they need JSBI support?

Having the source use native BigInt convergent and ages well.

[12wrigja]

From that plugin's README:

It will try to detect when an operator is used for bigints, not numbers. This will not work in many cases, so please use JSBI directly only if you know, that the code works only with bigints.

This is type-aware emit, and (from experience rewriting from using big-integer to JSBI) this would be likely too hard for Babel to detect (though easy for tsc to detect, but it's too late at the point this plugin runs).

[Pyrolistical]

@12wrigja but the neat thing for our use-case is, we only need to verify that babel can detect all the uses in this polyfill specifically and rewrite parts to make it more possible. we do not have the general problem of detecting all possible uses of native BigInt

[12wrigja]

verify that babel can detect all the uses

I remain skeptical this can be done correctly.