Why tslib as dependency?

[atassis]

You shouldn't rely on tslib at all, it is a typescript compilation level helper, as documented on its side. I saw that by checking dependencies on my server code. We don't use importHelpers flag, it is totally unnecessary in any kind of environment, but still its the single dependency you have

RxJS version:
6.x and higher

Expected behavior:
tslib not being listed as dependency at all

Actual behavior:
tslib as dependency

Additional information:
https://github.com/Microsoft/tslib

[kwonoj]

rxjs itself currently uses importhelpers

rxjs/src/tsconfig.esm.json

Line 5 in 9e9064b

"importHelpers": true,

and try to dedupe runtime code generated by tsc per each files. There are some internal discussion around if we should get away from it or not after re-do size benchmark.

It was introduced due to benefit of tslib

this can avoid duplicate declarations of things like __extends, __assign, etc., this means delivering users smaller files on average, as well as less runtime overhead. For optimized bundles with TypeScript, you should absolutely consider using tslib and --importHelpers.

in lib itself.

it is a typescript compilation level helper

I'm curios to hear more about this - tslib pkg itself says it's This is a runtime library for tsc builds and we use it for those purpose.

[kwonoj]

And I'm moving this into discussions as issues are for core team's backlog for bug tracking.

[benlesh]

I think by version 8 we might be able to remove this. Really we have this in place to support IE and older versions of Node.

[kwonoj]

One another reason at the moment was it reduced total bytesize by consolidating boilerplate. I do not know if that's still the case, and would like to remove tslib as well if possible.