move transformers over to using ast-types when constructing new nodes

lib/6to5/transformers/classes.js

@@ -1,5 +1,6 @@
 var traverse = require("../traverse");
 var util     = require("../util");
+var b        = require("ast-types").builders;
 var _        = require("lodash");
 
 exports.ClassDeclaration = function (node) {
@@ -47,7 +48,7 @@ var buildClassBody = function (body, className, superName, node) {
       if (node.kind === "") {
         addConstructor(body[0], method);
       } else {
-        throw new Error("unknown kind for constructor method");
+        throw util.errorWithNode(node, "unknown kind for constructor method");
       }
     } else {
       if (node.kind === "") {
@@ -69,29 +70,27 @@ var buildClassBody = function (body, className, superName, node) {
 
 var superIdentifier = function (superName, node, parent) {
   if (parent.property === node) return;
-  if (!superName) return;
 
-  node.name = superName.name;
+  node.name = superName.name || superName.value;
 
   // super(); -> ClassName.call(this);
   if (parent.type === "CallExpression" && parent.callee === node) {
     node.name += ".call";
-    parent.arguments.unshift({
-      type: "ThisExpression"
-    });
+    parent.arguments.unshift(b.thisExpression());
   }
 };
 
 var replaceInstanceSuperReferences = function (superName, method) {
+  superName = superName || b.literal("Function");
+
   traverse(method, function (node, parent) {
     if (node.type === "Identifier" && node.name === "super") {
       superIdentifier(superName, node, parent);
     } else if (node.type === "MemberExpression") {
       // no accessing of super properties
 
-
       if (isAccessingSuperProperties(parent, node)) {
-        throw new Error("cannot access super properties");
+        throw util.errorWithNode(node, "cannot access super properties");
       } else {
         return;
       }
@@ -101,16 +100,10 @@ var replaceInstanceSuperReferences = function (superName, method) {
       if (callee.object.name !== "super") return;
 
       callee.property.name = "prototype." + callee.property.name + ".call";
-      node.arguments.unshift({
-        type: "ThisExpression"
-      });
+      node.arguments.unshift(b.thisExpression());
     } else {
       return;
     }
-
-    if (!superName) {
-      throw new Error("cannot access super as this class has none");
-    }
   });
 };