Fix typescript issues after latest release 7.1.0

[julienw]

With latest release 7.1.0, I had to install helmet as a dependency. This produced typescript errors (with all version of Helmet I tried):

koa-helmet/koa-helmet.d.ts

Line 11 in 884c4be

type HelmetOptions = helmet.HelmetOptions;

gives

node_modules/koa-helmet/koa-helmet.d.ts:11:22 - error TS2503: Cannot find namespace 'helmet'.

11 type HelmetOptions = helmet.HelmetOptions;
                        ~~~~~~

This is fixed easily enough by importing HelmetOptions directly instead.

But then we get another error:

node_modules/koa-helmet/koa-helmet.d.ts:70:38 - error TS2339: Property 'expectCt' does not exist on type 'HelmetOptions'.

70     expectCt(options?: HelmetOptions['expectCt']): Middleware;

That's happening because helmet removes expectCt and as a result this isn't available anymore. Helmet folks suggest to use the expect-ct package if needed, but I'm reluctant to add this as another peer-dependency if most users of koa-helmet don't need it.

So instead I'm using a mapped type to construct koa-helmet's default export. This should adapt koa-helmet's type with whatever helmet version a project uses.

I'm also using the JS module syntax instead of the common module syntax.

I also had to fix new typescript issues in the test file that were surfaced after this change, which proves that the change is beneficial.
This is probably a breaking change and will need a major update, but given 7.1.0 should have been a major update too, I'd say it's OK.

Please tell me what you think!

[julienw]

gently ping @venables :-)

[venables]

Thanks @julienw

[venables]

This has been included in v8.0.0. I apologize for the breaking change in 7.1.0, which also should have been a major release.

[julienw]

Thanks so much for the merge and the quick release!