try .ts extension

src/build.ts

@@ -11,7 +11,7 @@ import type {
   GqlContext,
   UnionType,
   InterfaceType,
-} from './types.js';
+} from './types.ts';
 
 export function buildGraphQLSchema<RootSrc>(
   schema: Schema<RootSrc>

src/define.ts

@@ -20,7 +20,7 @@ import type {
   SubscriptionObjectType,
   PromiseOrValue,
   GqlContext,
-} from './types.js';
+} from './types.ts';
 
 type ExtensionsMap = {
   field?: {

src/index.ts

@@ -1,7 +1,7 @@
-export type * from './types.js';
-export { Gql } from './define.js';
+export type * from './types.ts';
+export { Gql } from './define.ts';
 export {
   buildGraphQLSchema,
   toGraphQLInputType,
   toGraphQLOutputType,
-} from './build.js';
+} from './build.ts';

src/relay.ts

@@ -5,8 +5,8 @@ import type {
   TOfArgMap,
   GqlContext,
   ObjectType,
-} from './types.js';
-import { Gql } from './define.js';
+} from './types.ts';
+import { Gql } from './define.ts';
 import { GraphQLResolveInfo } from 'graphql';
 
 // Adapted from

test-api/api.ts

@@ -1,6 +1,6 @@
-import { Gql, ObjectType } from '../src';
+import { Gql, ObjectType } from '../src/index.ts';
 
-declare module '../src/types' {
+declare module '../src/types.ts' {
   interface Context {
     contextContent: string;
   }

tsconfig.json

@@ -2,7 +2,7 @@
   "compilerOptions": {
     "target": "ES2019",
     "module": "ESNext",
-    "moduleResolution": "node",
+    "moduleResolution": "NodeNext",
     "rootDir": "src",
     "outDir": "dist",
     "declaration": true,
@@ -13,7 +13,8 @@
     "noUnusedParameters": true,
     "noImplicitReturns": true,
     "noFallthroughCasesInSwitch": true,
-    "skipLibCheck": true
+    "skipLibCheck": true,
+    "allowImportingTsExtensions": true,
   },
   "files": ["./src/index.ts", "./src/relay.ts"]
 }