fix(handler type): make callback parameter optional (#222)

Author: ercgrat

src/function/handler.ts

@@ -8,7 +8,7 @@ export interface HandlerCallback<ResponseType extends Response = Response> {
 }
 
 export interface BaseHandler<ResponseType extends Response = Response, C extends Context = Context> {
-  (event: Event, context: C, callback: HandlerCallback<ResponseType>): void | ResponseType | Promise<ResponseType>
+  (event: Event, context: C, callback?: HandlerCallback<ResponseType>): void | ResponseType | Promise<ResponseType>
 }
 
 export type Handler = BaseHandler<Response, Context>

src/lib/builder.ts

@@ -21,7 +21,7 @@ const augmentResponse = (response: BuilderResponse) => {
 const wrapHandler =
   (handler: BuilderHandler): Handler =>
   // eslint-disable-next-line promise/prefer-await-to-callbacks
-  (event: HandlerEvent, context: HandlerContext, callback: HandlerCallback<Response>) => {
+  (event: HandlerEvent, context: HandlerContext, callback?: HandlerCallback<Response>) => {
     if (event.httpMethod !== 'GET' && event.httpMethod !== 'HEAD') {
       return Promise.resolve({
         body: 'Method Not Allowed',
@@ -37,7 +37,7 @@ const wrapHandler =
     }
 
     // eslint-disable-next-line promise/prefer-await-to-callbacks
-    const wrappedCallback = (error: unknown, response: BuilderResponse) => callback(error, augmentResponse(response))
+    const wrappedCallback = (error: unknown, response: BuilderResponse) => callback?.(error, augmentResponse(response))
     const execution = handler(modifiedEvent, context, wrappedCallback)
 
     if (isPromise(execution)) {