Use DTS by default only if module_type is set, prevents breaking proj…

…ects that can't handle "export" keyword.

lib/js_routes.rb

@@ -41,19 +41,26 @@ def generate!(file_name = configuration.file, **opts)
 
     sig { params(opts: T.untyped).returns(String) }
     def definitions(**opts)
-      generate(**opts, module_type: 'DTS',)
+      generate(**opts, module_type: default_module_type,)
     end
 
     sig { params(file_name: FileName, opts: T.untyped).void }
     def definitions!(file_name = nil, **opts)
       file_name ||= configuration.file&.sub(%r{(\.d)?\.(j|t)s\Z}, ".d.ts")
-      generate!(file_name, **opts, module_type: 'DTS')
+      generate!(file_name, **opts, module_type: default_module_type)
     end
 
     sig { params(value: T.untyped).returns(String) }
     def json(value)
       ActiveSupport::JSON.encode(value)
     end
+
+    sig { returns(T.nilable(String)) }
+    def default_module_type
+      'DTS' if configuration.module_type
+    end
+
+
   end
   module Generators
   end

spec/js_routes/module_types/dts_spec.rb

@@ -122,5 +122,15 @@
       generated_js = JsRoutes.definitions(**options)
       expect(generated_js).to include('export {};')
     end
+
+    it 'does not use DTS module if module_type is not set' do
+      previous_module_type = JsRoutes.configuration.module_type
+      JsRoutes.configuration.module_type = nil
+
+      generated_js = JsRoutes.definitions(**options.merge(module_type: nil))
+      expect(generated_js).not_to include('export {};')
+
+      JsRoutes.configuration.module_type = previous_module_type
+    end
   end
 end