Merge pull request #1256 from jayphelps/fix-writable

class properties with an undefined value are now correctly writable

src/babel/transformation/transformers/es6/classes.js

@@ -552,6 +552,11 @@ class ClassTransformer {
         this.instancePropBody.push(t.expressionStatement(
           t.assignmentExpression("=", t.memberExpression(t.thisExpression(), node.key), node.value)
         ));
+
+        node.value = null;
+      }
+
+      if (!node.value) {
         node.value = t.identifier("undefined");
       }
 

test/core/fixtures/transformation/es7.class-properties/instance-undefined/actual.js

@@ -0,0 +1,3 @@
+class Foo {
+  bar;
+}

test/core/fixtures/transformation/es7.class-properties/instance-undefined/expected.js

@@ -0,0 +1,14 @@
+"use strict";
+
+var Foo = (function () {
+  function Foo() {
+    babelHelpers.classCallCheck(this, Foo);
+  }
+
+  babelHelpers.createClass(Foo, [{
+    key: "bar",
+    value: undefined,
+    enumerable: true
+  }]);
+  return Foo;
+})();

test/core/fixtures/transformation/es7.class-properties/static-undefined/actual.js

@@ -0,0 +1,3 @@
+class Foo {
+  static bar;
+}

test/core/fixtures/transformation/es7.class-properties/static-undefined/exec.js

@@ -0,0 +1,6 @@
+class Foo {
+  static num;
+}
+
+assert.equal("num" in Foo, true);
+assert.equal(Foo.num, undefined);

test/core/fixtures/transformation/es7.class-properties/static-undefined/expected.js

@@ -0,0 +1,14 @@
+"use strict";
+
+var Foo = (function () {
+  function Foo() {
+    babelHelpers.classCallCheck(this, Foo);
+  }
+
+  babelHelpers.createClass(Foo, null, [{
+    key: "bar",
+    value: undefined,
+    enumerable: true
+  }]);
+  return Foo;
+})();