don't use function variable declaration for class constructor

lib/6to5/generation/generator.js

@@ -125,7 +125,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
 
     var lines = 0;
 
-    if (node.start != null) {
+    if (node.start != null && !node._ignoreUserWhitespace) {
       // user node
       if (leading) {
         lines = self.whitespace.getNewlinesBefore(node);

lib/6to5/generation/node/whitespace.js

@@ -62,11 +62,15 @@ _.each({
   CallExpression: { after: 1 },
   Literal: { after: 1 }
 }, function (amounts, type) {
-  if (_.isNumber(amounts)) amounts = { after: amounts, before: amounts };
+  if (_.isNumber(amounts)) {
+    amounts = { after: amounts, before: amounts };
+  }
 
-  _.each(amounts, function (amount, key) {
-    exports[key].nodes[type] = function () {
-      return amount;
-    };
-  });
+  _.each([type].concat(t.FLIPPED_ALIAS_KEYS[type] || []), function (type) {
+    _.each(amounts, function (amount, key) {
+      exports[key].nodes[type] = function () {
+        return amount;
+      };
+    });
+  })
 });

lib/6to5/transformation/transformers/es6-classes.js

@@ -50,14 +50,18 @@ Class.prototype.run = function () {
 
   var body = this.body = [];
 
-  var constructor = t.functionExpression(null, [], t.blockStatement([]));
-  if (this.node.id) constructor.id = className;
+  var constructor;
+  if (this.node.id) {
+    constructor = t.functionDeclaration(className, [], t.blockStatement([]));
+    body.push(constructor);
+  } else {
+    constructor = t.functionExpression(null, [], t.blockStatement([]));
+    body.push(t.variableDeclaration("var", [
+      t.variableDeclarator(className, constructor)
+    ]));
+  }
   this.constructor = constructor;
 
-  body.push(t.variableDeclaration("let", [
-    t.variableDeclarator(className, constructor)
-  ]));
-
   var closureArgs = [];
   var closureParams = [];
 
@@ -85,7 +89,7 @@ Class.prototype.run = function () {
 
   if (body.length === 1) {
     // only a constructor so no need for a closure container
-    init = constructor;
+    init = t.toExpression(constructor);
   } else {
     body.push(t.returnStatement(className));
     init = t.callExpression(
@@ -294,8 +298,9 @@ Class.prototype.pushConstructor = function (method) {
   t.inherits(construct, fn);
   t.inheritsComments(construct, method);
 
-  construct.defaults = fn.defaults;
-  construct.params   = fn.params;
-  construct.body     = fn.body;
-  construct.rest     = fn.rest;
+  construct._ignoreUserWhitespace = true;
+  construct.defaults              = fn.defaults;
+  construct.params                = fn.params;
+  construct.body                  = fn.body;
+  construct.rest                  = fn.rest;
 };

lib/6to5/types/builder-keys.json

@@ -9,6 +9,7 @@
   "ExpressionStatement":     ["expression"],
   "File":                    ["program", "comments", "tokens"],
   "FunctionExpression":      ["id", "params", "body", "generator"],
+  "FunctionDeclaration":     ["id", "params", "body", "generator"],
   "Identifier":              ["name"],
   "IfStatement":             ["test", "consequent", "alternate"],
   "ImportDeclaration":       ["specifiers", "source"],

lib/6to5/types/index.js

@@ -307,6 +307,31 @@ t.toStatement = function (node, ignore) {
   return node;
 };
 
+/**
+ * Description
+ *
+ * @param {Object} node
+ * @returns {Object}
+ */
+
+exports.toExpression = function (node) {
+  if (t.isExpressionStatement(node)) {
+    node = node.expression;
+  }
+
+  if (t.isClass(node)) {
+    node.type = "ClassExpression";
+  } else if (t.isFunction(node)) {
+    node.type = "FunctionExpression";
+  }
+
+  if (t.isExpression(node)) {
+    return node;
+  } else {
+    throw new Error("cannot turn " + node.type + " to an expression");
+  }
+};
+
 /**
  * Description
  *