add util.ensureExpressionType which will change a node from a declaration to an expression

lib/6to5/transformers/let-scoping.js

@@ -44,7 +44,7 @@ exports.VariableDeclaration = function (node, parent, file) {
         };
 
         if (node.type === "FunctionDeclaration") {
-          node.type = "FunctionExpression";
+          util.ensureExpressionType(node);
           var declar = b.variableDeclaration("var", [
             b.variableDeclarator(node.id, callNode())
           ]);

lib/6to5/transformers/modules.js

@@ -72,11 +72,7 @@ var pushExportDeclaration = function (node, parent, nodes) {
   var declar = node.declaration;
 
   if (node.default) {
-    if (declar.type === "FunctionDeclaration") {
+    util.ensureExpressionType(declar);
-      declar.type = "FunctionExpression";
-    } else if (declar.type === "ClassDeclaration") {
-      declar.type = "ClassExpression";
-    }
 
     nodes.push(util.template("exports-default", {
       VALUE: declar

lib/6to5/util.js

@@ -24,6 +24,14 @@ exports.list = function (val) {
   return val ? val.split(",") : [];
 };
 
+exports.ensureExpressionType = function (node) {
+  node.type = {
+    FunctionDeclaration: "FunctionExpression",
+    ClassDeclaration: "ClassExpression"
+  }[node.type] || node.type;
+  return node;
+};
+
 exports.getUid = function (parent, file) {
   var node;