Is there a way to specify function type with an arrow function?-CodePudding

Im using express and i know you can do the following to set teh type of the reques handler.

router.get("/", <RequestHandler> function (req, res, next) {
  //Manage request here
});

Is there a way to do the same with arrow functions? I know I can just specify the type of each param but thats a bit verbose I think.

I know this works

router.get("/", (req: Request, res: Response, next: NextFunction) => {
  //Manage request here
});

But could something like this work?

router.get("/", <RequestHandler>(req, res, next) => {
  //Manage request here
});

I get the following error for every parameter.

Parameter 'req' implicitly has an 'any' type.

CodePudding user response：

With an arrow function, you must surround the whole function expression in parentheses to avoid syntactical issues.

router.get("/", <RequestHandler>((req, res, next) => {
  //Manage request here
}));

Another option with as

router.get(
  "/",
  ((req, res, next) => {
  //Manage request here
  }) as RequestHandler
)

Another option, declare the callback as a standalone variable beforehand, avoiding type assertions entirely

const callback: RequestHandler = (req, res, next) => {
  //Manage request here
} as RequestHandler;

router.get("/", RequestHandler);

CodePudding user response：

If you are on Typescript 4.9 , you could make use of the satisfies keyword:

interface AddFunc {
    (a: number, b: number): number;
}

const add = ((a, b) => {
    return a   b
}) satisfies AddFunc;

CodePudding user response：

Try doing this: <RequestHandler<{type1; type2; type3}>> Or you can create a separate interface