createResponse simplified and safe against using as ResponseHandler

src/AutoRouter.ts

@@ -1,10 +1,8 @@
+import { RouteHandler } from 'IttyRouter'
+import { ResponseHandler, Router, RouterOptions } from './Router'
 import { error } from './error'
 import { json } from './json'
 import { withParams } from './withParams'
-import { Router, RouterOptions} from './Router'
-import { RouteHandler } from 'IttyRouter'
-import { ResponseFormatter } from './createResponse'
-import { ResponseHandler } from './Router'
 
 type AutoRouterOptions = {
   missing?: RouteHandler

src/IttyRouter.ts

@@ -39,7 +39,7 @@ export type RouteEntry = [
 ]
 
 // this is the generic "Route", which allows per-route overrides
-export type Route = <RequestType = IRequest, Args extends any[] = any[], RT = RouterType>(
+export type Route = <RequestType = IRequest, Args extends any[] = any[], RT = IttyRouterType>(
   path: string,
   ...handlers: RouteHandler<RequestType, Args>[]
 ) => RT

src/createResponse.spec.ts

@@ -59,11 +59,12 @@ describe('createResponse(mimeType: string, transform?: Function)', () => {
     expect(body).toBe('***')
   })
 
-  it('will ignore a Response, to allow downstream use', async () => {
+  it('will ignore a Response, to allow downstream use (will not modify headers)', async () => {
     const r1 = json({ foo: 'bar' })
-    const r2 = json(r1)
+    const r2 = text(r1)
 
     expect(r2).toBe(r1)
+    expect(r2.headers.get('content-type')?.includes('text')).toBe(false)
   })
 
   it('will ignore an undefined body', async () => {

src/createResponse.ts

@@ -6,21 +6,15 @@ export interface BodyTransformer {
   (body: any): string
 }
 
-export const createResponse =
+ export const createResponse =
   (
     format = 'text/plain; charset=utf-8',
     transform?: BodyTransformer
   ): ResponseFormatter =>
-  (body, { ...options } = {}) =>
-    body === undefined || body instanceof Response // skip function if undefined or an existing Response
-    ? body
-    : new Response(transform ? transform(body) : body, {
-                    ...options,
-                    headers: {
-                      'content-type': format,
-                      ...options.headers?.entries
-                          // @ts-expect-error - foul
-                          ? Object.fromEntries(options.headers)
-                          : options.headers
-                    },
-                  })
+  (body, { ...options } = {}) => {
+    if (body === undefined || body instanceof Response) return body
+
+    const response = new Response(transform?.(body) ?? body, options)
+    response.headers.set('content-type', format)
+    return response
+  }

tsconfig.json

@@ -10,10 +10,10 @@
     "lib": ["esnext", "dom", "dom.iterable"],
     "listEmittedFiles": false,
     "listFiles": false,
-    "moduleResolution": "nodeNext",
     "noFallthroughCasesInSwitch": true,
     "pretty": true,
-    "resolveJsonModule": true,
+    // "moduleResolution": "nodeNext",  // disabled to be compatible with module: "esnext"
+    // "resolveJsonModule": true,       // disabled to be compatible with module: "esnext"
     "rootDir": "src",
     "skipLibCheck": true,
     "strict": true,