Fixed import of files with nonstandard extensions (e.g. jsx) in default config

* Fixes #188

Author: sgravrock

lib/loader.js

@@ -18,7 +18,20 @@ Loader.prototype.load = function(modulePath) {
     return this.import_(url)
       .then(
         mod => mod.default,
-        e => Promise.reject(fixupImportException(e, modulePath))
+        e => {
+          if (e.code === 'ERR_UNKNOWN_FILE_EXTENSION') {
+            // Extension isn't supported by import, e.g. .jsx. Fall back to
+            // require(). This could lead to confusing error messages if someone
+            // tries to use ES module syntax without transpiling in a file with
+            // an unsupported extension, but it shouldn't break anything and it
+            // should work well in the normal case where the file is loadable
+            // as a CommonJS module, either directly or with the help of a
+            // loader like `@babel/register`.
+            return this.require_(modulePath);
+          } else {
+            return Promise.reject(fixupImportException(e, modulePath));
+          }
+        }
       );
   } else {
     return new Promise(resolve => {

spec/fixtures/import-jsx/jasmine.json

@@ -0,0 +1,7 @@
+{
+  "spec_dir": ".",
+  "spec_files": [
+    "spec.jsx"
+  ],
+  "helpers": []
+}

spec/fixtures/import-jsx/spec.jsx

@@ -0,0 +1,2 @@
+it('is a spec', function() {
+});

spec/integration_spec.js

@@ -65,6 +65,11 @@ describe('Integration', function () {
     expect(await runJasmine('spec/fixtures/js-loader-default')).toBeSuccess();
   });
 
+  it('falls back to require when loading extensions that import does not support', async function() {
+    expect(await runJasmine('spec/fixtures/import-jsx')).toBeSuccess();
+  });
+
+
   it('handles load-time exceptions from CommonJS specs properly', async function () {
     const {exitCode, output} = await runJasmine('spec/fixtures/cjs-load-exception');
     expect(exitCode).toEqual(1);

spec/loader_spec.js

@@ -19,6 +19,26 @@ describe('loader', function() {
         esModuleSharedExamples('js', true);
       });
 
+      describe('When the extnesion is not supported by import()', function() {
+        it('falls back to require()', async function() {
+          const error = new TypeError();
+          error.code = 'ERR_UNKNOWN_FILE_EXTENSION';
+          const payload = {};
+          const requireShim = jasmine.createSpy('requireShim')
+            .and.returnValue(Promise.resolve(payload));
+          const importShim = jasmine.createSpy('importShim')
+            .and.returnValue(Promise.reject(error));
+          const loader = new Loader({requireShim, importShim});
+          loader.alwaysImport = true;
+
+          const result = await loader.load('./spec.jsx');
+
+          expect(result).toBe(payload);
+          expect(requireShim).toHaveBeenCalled();
+          expect(importShim).toHaveBeenCalled();
+        });
+      });
+
       it('uses require to load JSON files', async function() {
         const requireShim = jasmine.createSpy('requireShim')
           .and.returnValue(Promise.resolve());