add eslint rules for promises #3796
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This ends up being a "bug fix" because it does remove an extra tick and so is observable. |
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For simplicity, I have dropped the specialized helpers, provider just a single |
...and enable basic rules
leads to one less tick in `executeStreamField` in the branch where completion of a non-promise yields a promise.
errors avoided by previously avoiding then/catch
we can't fix then, but we can replace it. instead of using immediately invoked anonymous asynchronous arrow functions, we can replace the then method with then-like helper functions. In fact, we can optimize these small helpers to the exact cases we need. = after() => helper with only onFulfilled callback = catchAfter => helper with onError callback that handles promise rejection = tryAfter => helper with synchronous onFulfilled callback and onError callback that handles promise rejection and onFulfilled exceptions
Motivation: It is faster to await a promise prior to returning it from an async function than to return a promise with `.then()`. See: https://github.com/tc39/proposal-faster-promise-adoption Previously, this eslint rule errored by default only 'in-try-catch'.
`after` becomes sync, requiring no return type check for the onFulfilled result.
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Closing this, see edited comment on #3754. The real world implications of the extra tick within |
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We could not demonstrate via actual benchmarking that the tick reduction from awaiting a promise prior to returning it translates into real-world performance gains. See graphql#3796. In any case, the promise must be awaited (irrespective of performance) to allow the catch block to handle rejection errors. Simply returning `completed` would result in test failures.
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We could not demonstrate via actual benchmarking that the tick reduction from awaiting a promise prior to returning it translates into real-world performance gains. See #3796. In any case, the promise must be awaited (irrespective of performance) to allow the catch block to handle rejection errors. Simply returning `completed` would result in test failures.
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UPDATE:
After much testing, I am unable to generalize the speed savings from #3754, so this PR has been closed.
See #3754 for further discussion.
prefer-await-over-promises helps avoid extra ticks, formalizing the optimization from #3754 across the board
various additional rules add additional best practices with regard to promise use with at most trivial code changes