koa: fix: Callback type to be compatible with node

[kf6kjg]

See definition of RequestListener at https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/node/http.d.ts#L115

The actual Koa code at https://github.com/koajs/koa/blob/master/lib/application.js#L168 does return a promise, but one that's already had both then and a generic catch called upon it.

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[typescript-bot]

@kf6kjg Thank you for submitting this PR!

This is a live comment which I will keep updated.

This PR doesn't modify any tests, so it's hard to know what's being fixed, and your changes might regress in the future. Have you considered adding tests to cover the change you're making? Including tests allows this PR to be merged by yourself and the owners of this module. This can potentially save days of time for you.

1 package in this PR

• koa on npm, on unpkg

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---

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[typescript-bot]

🔔 @DavidCai1993 @jkeylu @brikou @harryparkdotio @chatoo2412 — please review this PR in the next few days. Be sure to explicitly select Approve or Request Changes in the GitHub UI so I know what's going on.

[danger-public]

Inspecting the JavaScript source for this package found some properties that are not in the .d.ts files.
The check for missing properties isn't always right, so take this list as advice, not a requirement.

koa (unpkg)

was missing the following properties:

1. once
2. EventEmitter

Generated by 🚫 dangerJS against 02f3825

[typescript-bot]

👋 Hi there! I’ve run some quick measurements against master and your PR. These metrics should help the humans reviewing this PR gauge whether it might negatively affect compile times or editor responsiveness for users who install these typings.

Let’s review the numbers, shall we?

Comparison details 📊

	master	#48622	diff
Batch compilation
Memory usage (MiB)	70.5	71.1	+0.8%
Type count	10472	10472	0%
Assignability cache size	1805	1805	0%
Language service
Samples taken	200	200	0%
Identifiers in tests	200	200	0%
getCompletionsAtPosition
Mean duration (ms)	439.0	434.4	-1.0%
Mean CV	8.6%	8.3%
Worst duration (ms)	539.7	540.7	+0.2%
Worst identifier	Error	listen
getQuickInfoAtPosition
Mean duration (ms)	441.1	436.6	-1.0%
Mean CV	8.2%	8.3%	+1.6%
Worst duration (ms)	551.5	560.0	+1.5%
Worst identifier	listen	app

It looks like nothing changed too much. I won’t post performance data again unless it gets worse.

[orta]

Ping 🔔 @DavidCai1993 @jkeylu @brikou @harryparkdotio @chatoo2412

[harryparkdotio]

The actual Koa code at https://github.com/koajs/koa/blob/master/lib/application.js#L168 does return a promise, but one that's already had both then and a generic catch called upon it.

The response of the callback method is still a function which returns a Promise, having called then and catch on the Promise doesn't change the return type from being a Promise.

However, the function that callback returns (essentially a RequestListener), still handles a request using a callback style approach (which makes sense, given that the node RequestListener is a callback). This means that the Koa callback RequestListener, while it is still returning a Promise, the resolution of that Promise is bound to the middleware stack and is unrelated to the http callback. This is likely due to the need of resolving the entire middleware chain prior to initiating the http response callback.

While the Koa code does still return a Promise, I think this Promise is an internal concern incorrectly being exposed, and so treating callback as if nothing was returned (void) seems both valid and rational to me.

[typescript-bot]

@kf6kjg Everything looks good here. Great job! I am ready to merge this PR on your behalf.

If you'd like that to happen, please post a comment saying:

Ready to merge

and I'll merge this PR almost instantly. Thanks for helping out! ❤️

(@DavidCai1993, @jkeylu, @brikou, @harryparkdotio, @chatoo2412: you can do this too.)

[kf6kjg]

Ready to merge

[typescript-bot]

I just published @types/koa@2.11.6 to npm.