just return constructor if only a constructor exists in classes

lib/6to5/transformers/classes.js

@@ -42,10 +42,9 @@ var buildClass = function (node, file) {
 
   var block     = container.callee.body;
   var body      = block.body;
+  var construct = body[0].declarations[0].init;
 
-  if (node.id) {
-    body[0].declarations[0].init.id = className;
-  }
+  if (node.id) construct.id = className;
 
   var returnStatement = body.pop();
 
@@ -56,19 +55,22 @@ var buildClass = function (node, file) {
     container.callee.params.push(superClassCallee);
   }
 
-  buildClassBody(body, className, superName, node);
+  buildClassBody(construct, body, className, superName, node);
 
-  body.push(returnStatement);
-
-  return container;
+  if (body.length === 1) {
+    // only a constructor so no need for a closure container
+    return construct;
+  } else {
+    body.push(returnStatement);
+    return container;
+  }
 };
 
-var buildClassBody = function (body, className, superName, node) {
+var buildClassBody = function (construct, body, className, superName, node) {
   var instanceMutatorMap = {};
   var staticMutatorMap   = {};
   var hasConstructor     = false;
 
-  var construct = body[0].declarations[0].init;
   var classBody = node.body.body;
 
   _.each(classBody, function (node) {
@@ -127,21 +129,21 @@ var superIdentifier = function (superName, methodNode, methodName, node, parent)
 
     if (methodName === "constructor") {
       // constructor() { super(); }
-      return b.memberExpression(superName, b.identifier("call"), false);
+      return b.memberExpression(superName, b.identifier("call"));
     } else {
       node = superName;
 
       // foo() { super(); }
       if (!methodNode.static) {
-        node = b.memberExpression(node, b.identifier("prototype"), false);
+        node = b.memberExpression(node, b.identifier("prototype"));
       }
 
-      node = b.memberExpression(node, b.identifier(methodName), false);
-      return b.memberExpression(node, b.identifier("call"), false);
+      node = b.memberExpression(node, b.identifier(methodName));
+      return b.memberExpression(node, b.identifier("call"));
     }
   } else if (parent.type === "MemberExpression" && !methodNode.static) {
     // super.test -> ClassName.prototype.test
-    return b.memberExpression(superName, b.identifier("prototype"), false);
+    return b.memberExpression(superName, b.identifier("prototype"));
   } else {
     return superName;
   }