Added the __esModule export, with value true, when the format is cjs or umd, and the exports option is named.

src/finalisers/cjs.js

@@ -34,5 +34,9 @@ export default function cjs ( bundle, magicString, { exportMode }, options ) {
 	const exportBlock = getExportBlock( bundle.entryModule, exportMode, 'module.exports =' );
 	if ( exportBlock ) magicString.append( '\n\n' + exportBlock );
 
+	if (exportMode === 'named') {
+		magicString.append('\n\nexports.__esModule = true;\n\n');
+	}
+
 	return magicString;
 }

src/finalisers/umd.js

@@ -69,6 +69,10 @@ export default function umd ( bundle, magicString, { exportMode, indentString },
 	const exportBlock = getExportBlock( bundle.entryModule, exportMode );
 	if ( exportBlock ) magicString.append( '\n\n' + exportBlock );
 
+	if (exportMode === 'named') {
+		magicString.append('\n\nexports.__esModule = true;\n\n');
+	}
+
 	return magicString
 		.trim()
 		.indent( indentString )

test/form/assignment-to-exports-class-declaration/_expected/cjs.js

@@ -2,3 +2,5 @@
 
 exports.Foo = class Foo {}
 exports.Foo = lol( exports.Foo );
+
+exports.__esModule = true;

test/form/assignment-to-exports-class-declaration/_expected/umd.js

@@ -7,4 +7,6 @@
 	exports.Foo = class Foo {}
 	exports.Foo = lol( exports.Foo );
 
+	exports.__esModule = true;
+
 }));

test/form/computed-properties/_expected/cjs.js

@@ -14,4 +14,6 @@ class X {
 }
 
 exports.x = x;
-exports.X = X;
+exports.X = X;
+
+exports.__esModule = true;

test/form/computed-properties/_expected/umd.js

@@ -20,4 +20,6 @@
 	exports.x = x;
 	exports.X = X;
 
-}));
+	exports.__esModule = true;
+
+}));

test/form/dedupes-external-imports/_expected/cjs.js

@@ -30,3 +30,5 @@ const baz = new Baz();
 exports.foo = foo;
 exports.bar = bar;
 exports.baz = baz;
+
+exports.__esModule = true;

test/form/dedupes-external-imports/_expected/umd.js

@@ -33,4 +33,6 @@
 	exports.bar = bar;
 	exports.baz = baz;
 
-}));
+	exports.__esModule = true;
+
+}));

test/form/export-all-from-internal/_expected/cjs.js

@@ -5,3 +5,5 @@ const b = 2;
 
 exports.a = a;
 exports.b = b;
+
+exports.__esModule = true;

test/form/export-all-from-internal/_expected/umd.js

@@ -10,4 +10,6 @@
 	exports.a = a;
 	exports.b = b;
 
-}));
+	exports.__esModule = true;
+
+}));

test/form/export-default-import/_expected/cjs.js

@@ -6,4 +6,6 @@ var x = _interopDefault(require('x'));
 
 
 
-exports.x = x;
+exports.x = x;
+
+exports.__esModule = true;

test/form/export-default-import/_expected/umd.js

@@ -10,4 +10,6 @@
 
 	exports.x = x;
 
-}));
+	exports.__esModule = true;
+
+}));

test/form/exports-at-end-if-possible/_expected/cjs.js

@@ -7,3 +7,5 @@ console.log( FOO );
 console.log( FOO );
 
 exports.FOO = FOO;
+
+exports.__esModule = true;

test/form/exports-at-end-if-possible/_expected/umd.js

@@ -12,4 +12,6 @@
 
 	exports.FOO = FOO;
 
-}));
+	exports.__esModule = true;
+
+}));

test/form/multiple-exports/_expected/cjs.js

@@ -5,3 +5,5 @@ var bar = 2;
 
 exports.foo = foo;
 exports.bar = bar;
+
+exports.__esModule = true;

test/form/multiple-exports/_expected/umd.js

@@ -10,4 +10,6 @@
 	exports.foo = foo;
 	exports.bar = bar;
 
-}));
+	exports.__esModule = true;
+
+}));

test/form/namespaced-named-exports/_expected/cjs.js

@@ -2,4 +2,6 @@
 
 var answer = 42;
 
-exports.answer = answer;
+exports.answer = answer;
+
+exports.__esModule = true;

test/form/namespaced-named-exports/_expected/umd.js

@@ -8,4 +8,6 @@
 
 	exports.answer = answer;
 
-}));
+	exports.__esModule = true;
+
+}));

test/form/no-treeshake/_expected/cjs.js

@@ -23,3 +23,5 @@ exports.baz = baz;
 exports.create = create;
 exports.getPrototypeOf = getPrototypeOf;
 exports.strange = quux;
+
+exports.__esModule = true;

test/form/no-treeshake/_expected/umd.js

@@ -26,4 +26,6 @@
 	exports.getPrototypeOf = getPrototypeOf;
 	exports.strange = quux;
 
+	exports.__esModule = true;
+
 }));

test/form/preserves-comments-after-imports/_expected/cjs.js

@@ -7,3 +7,5 @@ var number = 5;
 var obj = { number };
 
 exports.obj = obj;
+
+exports.__esModule = true;

test/form/preserves-comments-after-imports/_expected/umd.js

@@ -12,4 +12,6 @@
 
 	exports.obj = obj;
 
-}));
+	exports.__esModule = true;
+
+}));

test/form/umd-noconflict/_expected/cjs.js

@@ -10,4 +10,6 @@ var setting = 'no';
 
 exports.doThings = doThings;
 exports.number = number;
-exports.setting = setting;
+exports.setting = setting;
+
+exports.__esModule = true;

test/form/umd-noconflict/_expected/umd.js

@@ -21,4 +21,6 @@
 	exports.number = number;
 	exports.setting = setting;
 
+	exports.__esModule = true;
+
 }));

test/function/deconflicts-exports/_config.js

@@ -3,7 +3,7 @@ var assert = require( 'assert' );
 module.exports = {
 	description: 'renames variables named `exports` if necessary',
 	exports: function ( exports ) {
-		assert.deepEqual( Object.keys( exports ), [ 'a', 'b' ] );
+		assert.deepEqual( Object.keys( exports ), [ 'a', 'b', '__esModule' ] );
 		assert.equal( exports.a, 'A' );
 		assert.equal( exports.b, 42 );
 	}

test/function/export-destruction/_config.js

@@ -5,7 +5,7 @@ module.exports = {
 	babel: true,
 
 	exports: function ( exports ) {
-		assert.deepEqual( Object.keys( exports ), [ 'baz', 'quux' ] );
+		assert.deepEqual( Object.keys( exports ), [ 'baz', 'quux', '__esModule' ] );
 		assert.equal( exports.baz, 5 );
 		assert.equal( exports.quux, 17 );
 	}