Set TypeScript option esModuleInterop to true by default (#971)

Author: fathyb

package.json

@@ -88,7 +88,7 @@
     "sinon": "^4.2.2",
     "sourcemap-validator": "^1.0.6",
     "stylus": "^0.54.5",
-    "typescript": "^2.6.2"
+    "typescript": "^2.7.0"
   },
   "scripts": {
     "test": "cross-env NODE_ENV=test mocha",

src/assets/TypeScriptAsset.js

@@ -8,7 +8,11 @@ class TypeScriptAsset extends JSAsset {
     let transpilerOptions = {
       compilerOptions: {
         module: typescript.ModuleKind.CommonJS,
-        jsx: typescript.JsxEmit.Preserve
+        jsx: typescript.JsxEmit.Preserve,
+
+        // it brings the generated output from TypeScript closer to that generated by Babel
+        // see https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-7.html
+        esModuleInterop: true
       },
       fileName: this.relativeName
     };

test/integration/typescript-interop/commonjs-module.js

@@ -0,0 +1 @@
+module.exports = () => 'test passed'

test/integration/typescript-interop/index.ts

@@ -0,0 +1,3 @@
+import testModule from './commonjs-module'
+
+export const test = testModule

test/typescript.js

@@ -106,4 +106,24 @@ describe('typescript', function() {
     let file = fs.readFileSync(__dirname + '/dist/index.js', 'utf8');
     assert(file.includes('React.createElement("div"'));
   });
+
+  it('should use esModuleInterop by default', async function() {
+    let b = await bundle(
+      __dirname + '/integration/typescript-interop/index.ts'
+    );
+
+    assertBundleTree(b, {
+      name: 'index.js',
+      assets: ['index.ts', 'commonjs-module.js'],
+      childBundles: [
+        {
+          type: 'map'
+        }
+      ]
+    });
+
+    let output = run(b);
+    assert.equal(typeof output.test, 'function');
+    assert.equal(output.test(), 'test passed');
+  });
 });

yarn.lock

@@ -6087,7 +6087,7 @@ typedarray@^0.0.6:
   version "0.0.6"
   resolved "https://registry.yarnpkg.com/typedarray/-/typedarray-0.0.6.tgz#867ac74e3864187b1d3d47d996a78ec5c8830777"
 
-typescript@^2.6.2:
+typescript@^2.7.0:
   version "2.7.2"
   resolved "https://registry.yarnpkg.com/typescript/-/typescript-2.7.2.tgz#2d615a1ef4aee4f574425cdff7026edf81919836"