Question

Let’s suppose I’m defining a module, and I have some function definitions like this:

export function bodyParser(options?:any): 
  (req: ExpressServerRequest, res: ExpressServerResponse, next) =>void;
export function errorHandler(opts?:any): 
  (req: ExpressServerRequest, res: ExpressServerResponse, next) =>void;
export function methodOverride(): 
  (req: ExpressServerRequest, res: ExpressServerResponse, next) =>void;
export function favicon(url: string, opts? ): 
  (req: ExpressServerRequest, res: ExpressServerResponse, next) =>void;
export function logger(type: string, opts? ): 
  (req: ExpressServerRequest, res: ExpressServerResponse, next) =>void;

I’m repeatedly using this return type annotation:

(req: ExpressServerRequest, res: ExpressServerResponse, next) =>void

Is there a way to define that type, assign it a name, and just reference the name instead of repeating the same thing?

Answer 1

Yep! You can use an interface with a call signature:

interface MyCallSignature {
    (req: ExpressServerRequest, res: ExpressServerResponse, next): void;
}

Now you can use it like:

export function bodyParser(options?: any): MyCallSignature