SyntaxError: yield is a reserved word

[msageryd]

I get "SyntaxError: yield is a reserved word" from Prettier.

The function is a generator function used in a ReduxSaga:

function* saveUnsavedJournalItemsToServer() {
  const journalItemsToSave = yield select(selectCompletedUnsavedJournalItems);
  journalItemsToSave.map(journalItem => {
    yield call(saveJournalItemToServer, journalItem);
  });
}

Here is the complete output.

journalSagas.js: SyntaxError: yield is a reserved word (177:4)
  175 |
  176 |   journalItemsToSave.map(journalItem => {
> 177 |     yield call(saveJournalItemToServer, journalItem);
      |     ^
  178 |   });
  179 | }
  180 |

Is this a Prettier bug, or is my code flawed?

[k15a]

You call yield in a normal function but it is only allowed in a generator. I might be wrong but I think the correct code is:

function* saveUnsavedJournalItemsToServer() {
  const journalItemsToSave = yield select(selectCompletedUnsavedJournalItems);
  yield* journalItemsToSave.map(function* (journalItem) {
    yield call(saveJournalItemToServer, journalItem);
  });
}

[msageryd]

Ah, thanks.
That makes sense. Didn't see that I wrapped it in a normal function.

So, Prettier did a good job catching the problem. Maybe a better error message would be good, if possible.

[k15a]

That's the error message from either babel or flow because prettier uses them to parse your code. :)

If you want to learn more about generators take a look at http://exploringjs.com/es6/ch_generators.html

[msageryd]

Thanks again.
You guessed it: I'm a generator newbie =)

I'll read up some more on the subject. Also, the "yield call" will probably make funny stuff happen. I have now changed to "yield fork".

[msageryd]

This is maybe a rare occation where a good old for-loop comes in handy (instead of map or each). No messing around with nested generators needed.

[vjeux]

The error message is indeed super confusing. If you could open an issue on babylon and flow projects to get it improved that would be awesome!

[msageryd]

babel/babylon#530

I don't know if Flow would give this error as well. I don't use Flow anymore, so I presume it was Babel who gave the error.