Fix externals interop within SystemLibraryPlugin.

lib/library/SystemLibraryPlugin.js

@@ -116,6 +116,13 @@ class SystemLibraryPlugin extends AbstractLibraryPlugin {
 									Template.asString([
 										"function(module) {",
 										Template.indent(`${external} = module;`),
+										Template.indent([
+											"if (!Object.hasOwnProperty.call(module, '__esModule')) {",
+											Template.indent(
+												`Object.defineProperty(${external}, "__esModule", {value: true});`
+											),
+											"}"
+										]),
 										"}"
 									])
 								)

test/configCases/externals/externals-system/index.js

@@ -1,3 +1,5 @@
+import external3Default from 'external3';
+
 /* This test verifies that webpack externals are properly indicated as dependencies to System.
  * Also that when System provides the external variables to webpack that the variables get plumbed
  * through correctly and are usable by the webpack bundle.
@@ -8,4 +10,6 @@ it("should get an external from System", function() {
 
 	const external2 = require("external2");
 	expect(external2).toBe("the external2 value");
+
+	expect(external3Default).toBe("the external3 default export");
 });

test/configCases/externals/externals-system/test.config.js

@@ -4,7 +4,10 @@ module.exports = {
 	beforeExecute: () => {
 		System.init({
 			external1: "the external1 value",
-			external2: "the external2 value"
+			external2: "the external2 value",
+			external3: {
+				default: "the external3 default export",
+			}
 		});
 	},
 	moduleScope(scope) {

test/configCases/externals/externals-system/webpack.config.js

@@ -4,6 +4,7 @@ module.exports = {
 	},
 	externals: {
 		external1: "external1",
-		external2: "external2"
+		external2: "external2",
+		external3: "external3"
 	}
 };