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Add route-level generic Request/Response typing to TypeScript definitions #320

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Initial plan
Copilot Jun 1, 2026
92d7287
feat(types): add generic request and response route typings
Copilot Jun 1, 2026
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205 changes: 160 additions & 45 deletions index.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -44,21 +44,30 @@ export declare interface App {
[namespace: string]: Package;
}

export declare type Middleware = (
req: Request,
res: Response,
export declare type Middleware<
TRequest extends Request = Request,
TResponse extends Response = Response
> = (
req: TRequest,
res: TResponse,
next: NextFunction
) => void;
export declare type ErrorHandlingMiddleware = (
export declare type ErrorHandlingMiddleware<
TRequest extends Request = Request,
TResponse extends Response = Response
> = (
error: Error,
req: Request,
res: Response,
req: TRequest,
res: TResponse,
next: NextFunction
) => void;
export declare type ErrorCallback = (error?: Error) => void;
export declare type HandlerFunction = (
req: Request,
res: Response,
export declare type HandlerFunction<
TRequest extends Request = Request,
TResponse extends Response = Response
> = (
req: TRequest,
res: TResponse,
next?: NextFunction
) => void | any | Promise<any>;

Expand Down Expand Up @@ -196,7 +205,7 @@ export declare class Request {
[key: string]: any;
}

export declare class Response {
export declare class Response<TBody = any> {
status(code: number): this;

sendStatus(code: number): void;
Expand All @@ -219,11 +228,11 @@ export declare class Response {
callback?: ErrorCallback
): Promise<string>;

send(body: any): void;
send(body: TBody): void;

json(body: any): void;
json(body: TBody): void;

jsonp(body: any): void;
jsonp(body: TBody): void;

html(body: any): void;

Expand Down Expand Up @@ -269,62 +278,157 @@ export declare class API {
app(namespace: string, package: Package): App;
app(packages: App): App;

get(
get<TRequest extends Request = Request, TResponse extends Response = Response>(
path: string,
...middlewaresAndHandler: (Middleware | HandlerFunction)[]
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
get<TRequest extends Request = Request, TResponse extends Response = Response>(
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
get(...middlewaresAndHandler: (Middleware | HandlerFunction)[]): void;

post(
post<
TRequest extends Request = Request,
TResponse extends Response = Response
>(
path: string,
...middlewaresAndHandler: (Middleware | HandlerFunction)[]
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
post<
TRequest extends Request = Request,
TResponse extends Response = Response
>(
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
post(...middlewaresAndHandler: (Middleware | HandlerFunction)[]): void;

put(
put<TRequest extends Request = Request, TResponse extends Response = Response>(
path: string,
...middlewaresAndHandler: (Middleware | HandlerFunction)[]
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
put<TRequest extends Request = Request, TResponse extends Response = Response>(
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
put(...middlewaresAndHandler: (Middleware | HandlerFunction)[]): void;

patch(
patch<
TRequest extends Request = Request,
TResponse extends Response = Response
>(
path: string,
...middlewaresAndHandler: (Middleware | HandlerFunction)[]
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
patch<
TRequest extends Request = Request,
TResponse extends Response = Response
>(
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
patch(...middlewaresAndHandler: (Middleware | HandlerFunction)[]): void;

delete(
delete<
TRequest extends Request = Request,
TResponse extends Response = Response
>(
path: string,
...middlewaresAndHandler: (Middleware | HandlerFunction)[]
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
delete(...middlewaresAndHandler: HandlerFunction[]): void;

options(
delete<
TRequest extends Request = Request,
TResponse extends Response = Response
>(...middlewaresAndHandler: HandlerFunction<TRequest, TResponse>[]): void;

options<
TRequest extends Request = Request,
TResponse extends Response = Response
>(
path: string,
...middlewaresAndHandler: (Middleware | HandlerFunction)[]
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
options<
TRequest extends Request = Request,
TResponse extends Response = Response
>(
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
options(...middlewaresAndHandler: (Middleware | HandlerFunction)[]): void;

head(
head<TRequest extends Request = Request, TResponse extends Response = Response>(
path: string,
...middlewaresAndHandler: (Middleware | HandlerFunction)[]
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
head<TRequest extends Request = Request, TResponse extends Response = Response>(
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
head(...middlewaresAndHandler: (Middleware | HandlerFunction)[]): void;

any(
any<TRequest extends Request = Request, TResponse extends Response = Response>(
path: string,
...middlewaresAndHandler: (Middleware | HandlerFunction)[]
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
any<TRequest extends Request = Request, TResponse extends Response = Response>(
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
any(...middlewaresAndHandler: (Middleware | HandlerFunction)[]): void;

METHOD(
METHOD<
TRequest extends Request = Request,
TResponse extends Response = Response
>(
method: METHODS | METHODS[],
path: string,
...middlewaresAndHandler: (Middleware | HandlerFunction)[]
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;
METHOD(
METHOD<
TRequest extends Request = Request,
TResponse extends Response = Response
>(
method: METHODS | METHODS[],
...middlewaresAndHandler: (Middleware | HandlerFunction)[]
...middlewaresAndHandler: (
| Middleware<TRequest, TResponse>
| HandlerFunction<TRequest, TResponse>
)[]
): void;

register(
Expand All @@ -336,9 +440,20 @@ export declare class API {
routes(format: false): string[][];
routes(): string[][];

use(path: string, ...middleware: Middleware[]): void;
use(paths: string[], ...middleware: Middleware[]): void;
use(...middleware: (Middleware | ErrorHandlingMiddleware)[]): void;
use<TRequest extends Request = Request, TResponse extends Response = Response>(
path: string,
...middleware: Middleware<TRequest, TResponse>[]
): void;
use<TRequest extends Request = Request, TResponse extends Response = Response>(
paths: string[],
...middleware: Middleware<TRequest, TResponse>[]
): void;
use<TRequest extends Request = Request, TResponse extends Response = Response>(
...middleware: (
| Middleware<TRequest, TResponse>
| ErrorHandlingMiddleware<TRequest, TResponse>
)[]
): void;

finally(callback: FinallyFunction): void;

Expand Down
52 changes: 52 additions & 0 deletions index.test-d.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,23 @@ import {
ALBEvent,
} from 'aws-lambda';

type MetricsLogger = {
setProperty(name: string, value: boolean): void;
};

interface TypedRequest extends Request {
params: {
thingId: string;
anotherThingId: string;
};
context: Context & { metrics: MetricsLogger };
}

interface TypedResponseBody {
hello: string;
foo: string;
}

const options: Options = {
base: '/api',
version: 'v1',
Expand Down Expand Up @@ -174,6 +191,10 @@ expectType<void>(

expectType<void>(res.redirect('/new-path'));

const typedRes = {} as Response<TypedResponseBody>;
expectType<void>(typedRes.json({ hello: 'thing', foo: 'another-thing' }));
expectError(typedRes.json({ hello: 'thing' }));

const middleware: Middleware = (req, res, next) => {
next();
};
Expand All @@ -189,6 +210,37 @@ const handler: HandlerFunction = (req, res) => {
};
expectType<HandlerFunction>(handler);

const typedHandler: HandlerFunction<TypedRequest, Response<TypedResponseBody>> = (
req,
res
) => {
const { metrics } = req.context;
metrics.setProperty('test', true);
res.json({
hello: req.params.thingId,
foo: req.params.anotherThingId,
});
};
expectType<HandlerFunction<TypedRequest, Response<TypedResponseBody>>>(
typedHandler
);

api.get<TypedRequest, Response<TypedResponseBody>>('/typed', typedHandler);
const invalidTypedHandler: HandlerFunction<
TypedRequest,
Response<TypedResponseBody>
> = (req, res) => {
expectError(
res.json({
hello: req.params.thingId,
})
);
};
api.get<TypedRequest, Response<TypedResponseBody>>(
'/typed-invalid',
invalidTypedHandler
);

const cookieOptions: CookieOptions = {
domain: 'example.com',
httpOnly: true,
Expand Down
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