Polyfills are not generated from .browserslistrc queries

[ekb1zh]

My algorithm:

npx tsdx create mylib # run create new project and select "basic" option

cd mylib # go inside project

npm i # install packages

touch .browserslistrc # create file .browserslistrc

echo "dead" >> .browserslistrc # append query "dead" into .browserslistrc

> src/index.ts # clear src/index.ts

echo "export default () => { console.log(Object.fromEntries([[\"a\", 1]]), Promise.resolve(0)); }" >> src/index.ts # append code into src/index.ts

rm -r test # remove test folder with old code

npm run build # build project

cat dist/mylib.cjs.production.min.js # see result

Result - polyfills are absent. But they are need for execute code in dead browsers ))

These questions have been discussed in these threads .browserslistrc https://github.com/jaredpalmer/tsdx/issues/951, Object.fromEntries https://github.com/jaredpalmer/tsdx/issues/968, tslib https://github.com/jaredpalmer/tsdx/issues/412, but I didn't find an answer to the question - if targeting .browserslist file to the old browsers, should TSDX add polyfills?

• If yes, then this is not the case now.
• If not, so how would such code work in older browsers?

Note: If an incorrect request is entered into the .browserslist file, then an error will appear during the build, which means this file is included in the build, but why are polyfills not generated.

[agilgur5]

• If not, so how would such code work in older browsers?

Per https://github.com/jaredpalmer/tsdx/issues/968#issuecomment-791817207 , polyfills are currently out-of-scope for TSDX. They were planned per that answer but were never a part of TSDX outside of regenerator/async/await. That answer also mentions how polyfills in libraries are still a topic of discussion in the JS community. Adding the .browserslistrc as such will effectively tell @babel/preset-env to transform your code to as old as possible, but it won't insert polyfills for behavior that can't be transpiled down to an earlier environment.

The "suggested solution" in https://github.com/jaredpalmer/tsdx/issues/968#issuecomment-791817207 is still the suggested solution in this case, that would make corejs polyfills added. usage-pure means it won't pollute the consumer environment and many consumers already have corejs installed anyway, so that is my suggestion when it comes to the topic of polyfills in libraries. (Side note: babel-polyfills is also now a very stable collection of packages and is actually used under-the-hood of preset-env nowadays. I've also contributed a good bit to it and recently migrated it to TS)