Typescript definitions of nested function

Question

I am trying to create a type for my (nodejs)controller function like below

export const registerUser = asyncWrap(async function(req:Request, res:Response, next:NextFunction) {
    res.status(200).json({ success: true});
})

and the above code is fine, but I want to create a type so I can stop giving the type for the function params which is kinda redundant

What I've tried

type NormTyped = (fn:Promise<any>) => (req: Request, res: Response, next: NextFunction) => any;

export const registerUser:NormTyped = asyncWrap(async function(req, res, next) {
    res.status(200).json({ success: true});
})

But it gives me errors

Type '(...args: any) => Promise<any>' is not assignable to type 'NormTyped'.
  Type 'Promise<any>' is not assignable to type '(req: Request<ParamsDictionary, any, any, ParsedQs>,         res: Response<any>, next: NextFunction) => any'.
Type 'Promise<any>' provides no match for the signature '(req: Request<ParamsDictionary, any, any, ParsedQs>, res: Response<any>, next: NextFunction): any'.

This is how my asyncWrap looks like(in-case)

const asyncWrap = (fn: (...args: any) => any) =>
function asyncHandlerWrap(...args: any){
    const fnReturn = fn(...args)
    const next = args[args.length-1]
    return Promise.resolve(fnReturn).catch(next)
}

@Paul It is from @type/express which is just the type for the next middleware function — Thiti-Dev
– Thiti-Dev, Commented May 30, 2020 at 20:53

Thiti-Dev · Accepted Answer · 2020-05-31 09:13:50Z

1

Seem like typescript chooses to display the type of the one that defined in the function itself if provided so I ending up by defining the type directly in the asyncWrap like below

const asyncWrap = (fn: (req: Request,res: Response,next: NextFunction) => Promise<any>) =>
function asyncHandlerWrap(req: Request,res: Response,next: NextFunction){
    const fnReturn = fn(req,res,next)
    return Promise.resolve(fnReturn).catch(next)
}

answered May 31, 2020 at 9:13

Thiti-Dev

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Comments

Paul · Accepted Answer · 2020-05-30 21:02:15Z

0

NormTyped should be a function which accepts a function as an argument.

type NormTyped = (fn: (req: Request, res: Response, next: NextFunction) => any) => Promise<any>;

const asyncWrap = (fn: (...args: any) => any) =>
function asyncHandlerWrap(...args: any){
    const fnReturn = fn(...args)
    const next = args[args.length-1]
    return Promise.resolve(fnReturn).catch(next)
}

export const registerUser: NormTyped = asyncWrap(async function(req, res, next) {
    res.status(200).json({ success: true});
})

answered May 30, 2020 at 21:02

Paul

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1 Comment

Thiti-Dev Over a year ago

Tried it already, but the ts-linter still say that req, res, next are the type of any and it's not corresponding to the type above that declared

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