Add support for ESM - fixes #95

source/lib/config.ts

@@ -37,6 +37,7 @@ export default (pkg: {tsd?: RawConfig}, cwd: string): Config => {
 			lib: ['lib.es2017.d.ts'],
 			module: ModuleKind.CommonJS,
 			target: ScriptTarget.ES2017,
+			esModuleInterop: true,
 			...tsConfigCompilerOptions,
 			...packageJsonCompilerOptions,
 			moduleResolution: ModuleResolutionKind.NodeJs,

source/test/fixtures/esm/index.d.ts

@@ -0,0 +1,7 @@
+declare const one: {
+	(foo: string, bar: string): string;
+	(foo: number, bar: number): number;
+	<T extends string>(foo: T, bar: T): string;
+};
+
+export = one;

source/test/fixtures/esm/index.js

@@ -0,0 +1,3 @@
+const one = (foo, bar) => foo + bar;
+
+export default one;

source/test/fixtures/esm/index.test-d.ts

@@ -0,0 +1,4 @@
+import {expectType} from '../../../..';
+import one from './index.js';
+
+expectType<string>(one('foo', 'bar'));

source/test/fixtures/esm/package.json

@@ -0,0 +1,5 @@
+{
+	"name": "foo",
+	"type": "module",
+	"exports": "./index.js"
+}

source/test/test.ts

@@ -103,6 +103,14 @@ test('allow specifying a lib in tsconfig.json', async t => {
 	verify(t, diagnostics, []);
 });
 
+test('add support for esm with esModuleInterop', async t => {
+	const diagnostics = await tsd({
+		cwd: path.join(__dirname, 'fixtures/esm')
+	});
+
+	verify(t, diagnostics, []);
+});
+
 test('a lib option in package.json overrdides a lib option in tsconfig.json', async t => {
 	const diagnostics = await tsd({cwd: path.join(__dirname, 'fixtures/lib-config/lib-from-package-json-overrides-tsconfig-json')});