alekseykulikov/babel-preset-es2015-node5

Node 5 generator support incomplete

bmeck opened this issue · 8 comments

bmeck commented

see jbach/babel-preset-es2015-node4#1 , same issue persists in Node 5

alekseykulikov commented

Hm... this is really odd issue.

Personally, I use ES6 generators natively since node 0.11 and before this day, I thought it has no problem and it's one of the nicest features implemented natively.

I don't like the fact of compiling generators with regenerator and including special runtime, because of return bug. Also node's official documentation mentions generators as supported https://nodejs.org/en/docs/es6/.

Compact-table says node@5 covers 19/25 tests and babel+regenerator 22/25, and checks are a bit different, if we compile with regenerator, what's about generator.constructor for example?

For this preset, I want to use an official node documentation as a reference, and don't go too much in specification details. If they claim, that generators support is not full or should not be used natively, I will add it.

If you rely on .return and don't need native support, you can do:

{
  "presets": [
    "es2015-node5"
  ],
  "plugins": [
     "babel-plugin-transform-regenerator"
  ]
}
hax commented

I think it's possible to write a special transformer which only patch return for current V8 generators implementation, but I'm not sure I have enough time to do it now.

alekseykulikov commented

Agreed with @hax, special transformer similar to function-name would be a good solution.

hax commented

Initial implementation: https://github.com/hax/babel-plugin-transform-es2015-generator-return
I will test and publish it soon. 😃

hax commented

Tested and published!

You could add it to the preset 🏇

alekseykulikov commented

Awesome! I've just tested this module, and it wraps every generator to try/catch block and patches GeneratorPrototype. I still think, it should not be in a preset, since it may impact performance and make compiled code more verbose.
Maybe we should add a note to Readme instead?

hax commented

Try-catch will impact performance to normal function, but generators in V8 are not fully optimized anyway.
Check https://github.com/petkaantonov/bluebird/wiki/Optimization-killers you will see let/const also stop the function optimization. Consider this preset do not use transform-block-scope either, I think it's ok to add this plugin to preset 🎅

davej commented

Node 5 also doesn't support yield *, iterator closing. Which I believe is responsible for this issue: redux-saga/redux-saga#197