diff --git a/CLOBBER b/CLOBBER
index d2b7b9f7a637..763d9991e788 100644
--- a/CLOBBER
+++ b/CLOBBER
@@ -22,4 +22,4 @@
 # changes to stick? As of bug 928195, this shouldn't be necessary! Please
 # don't change CLOBBER for WebIDL changes any more.
 
-Bug 973238 part 8 needs clobber due to self-hosted code (bug 1019955).
+Bug 973238 part 9 needs clobber due to self-hosted code (bug 1019955).
diff --git a/js/src/builtin/SIMD.cpp b/js/src/builtin/SIMD.cpp
index 63a403e1698e..d460659acb31 100644
--- a/js/src/builtin/SIMD.cpp
+++ b/js/src/builtin/SIMD.cpp
@@ -51,7 +51,7 @@ static bool GetX4Lane(JSContext *cx, unsigned argc, Value *vp) {
 
     TypedObject &typedObj = args.thisv().toObject().as<TypedObject>();
     TypeDescr &descr = typedObj.typeDescr();
-    if (descr.kind() != TypeDescr::X4 || descr.as<X4TypeDescr>().type() != Type32x4::type) {
+    if (descr.kind() != type::X4 || descr.as<X4TypeDescr>().type() != Type32x4::type) {
         JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_INCOMPATIBLE_PROTO,
                              X4TypeDescr::class_.name, laneNames[lane],
                              InformalValueTypeName(args.thisv()));
@@ -94,7 +94,7 @@ static bool SignMask(JSContext *cx, unsigned argc, Value *vp) {
 
     TypedObject &typedObj = args.thisv().toObject().as<TypedObject>();
     TypeDescr &descr = typedObj.typeDescr();
-    if (descr.kind() != TypeDescr::X4 || descr.as<X4TypeDescr>().type() != Type32x4::type) {
+    if (descr.kind() != type::X4 || descr.as<X4TypeDescr>().type() != Type32x4::type) {
         JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_INCOMPATIBLE_PROTO,
                              X4TypeDescr::class_.name, "signMask",
                              InformalValueTypeName(args.thisv()));
@@ -216,7 +216,7 @@ CreateX4Class(JSContext *cx,
     if (!x4)
         return nullptr;
 
-    x4->initReservedSlot(JS_DESCR_SLOT_KIND, Int32Value(TypeDescr::X4));
+    x4->initReservedSlot(JS_DESCR_SLOT_KIND, Int32Value(type::X4));
     x4->initReservedSlot(JS_DESCR_SLOT_STRING_REPR, StringValue(stringRepr));
     x4->initReservedSlot(JS_DESCR_SLOT_ALIGNMENT, Int32Value(X4TypeDescr::size(type)));
     x4->initReservedSlot(JS_DESCR_SLOT_SIZE, Int32Value(X4TypeDescr::alignment(type)));
@@ -399,7 +399,7 @@ IsVectorObject(HandleValue v)
         return false;
 
     TypeDescr &typeRepr = obj.as<TypedObject>().typeDescr();
-    if (typeRepr.kind() != TypeDescr::X4)
+    if (typeRepr.kind() != type::X4)
         return false;
 
     return typeRepr.as<X4TypeDescr>().type() == V::type;
diff --git a/js/src/builtin/TypedObject.cpp b/js/src/builtin/TypedObject.cpp
index 556626d0f211..b7b3a41dec3f 100644
--- a/js/src/builtin/TypedObject.cpp
+++ b/js/src/builtin/TypedObject.cpp
@@ -1015,7 +1015,7 @@ StructMetaTypeDescr::create(JSContext *cx,
     if (!descr)
         return nullptr;
 
-    descr->initReservedSlot(JS_DESCR_SLOT_KIND, Int32Value(TypeDescr::Struct));
+    descr->initReservedSlot(JS_DESCR_SLOT_KIND, Int32Value(type::Struct));
     descr->initReservedSlot(JS_DESCR_SLOT_STRING_REPR, StringValue(stringRepr));
     descr->initReservedSlot(JS_DESCR_SLOT_ALIGNMENT, Int32Value(alignment));
     descr->initReservedSlot(JS_DESCR_SLOT_SIZE, Int32Value(totalSize.value()));
@@ -1120,13 +1120,13 @@ StructMetaTypeDescr::construct(JSContext *cx, unsigned int argc, Value *vp)
 }
 
 size_t
-StructTypeDescr::fieldCount()
+StructTypeDescr::fieldCount() const
 {
     return getReservedSlot(JS_DESCR_SLOT_STRUCT_FIELD_NAMES).toObject().getDenseInitializedLength();
 }
 
 bool
-StructTypeDescr::fieldIndex(jsid id, size_t *out)
+StructTypeDescr::fieldIndex(jsid id, size_t *out) const
 {
     JSObject &fieldNames = getReservedSlot(JS_DESCR_SLOT_STRUCT_FIELD_NAMES).toObject();
     size_t l = fieldNames.getDenseInitializedLength();
@@ -1141,14 +1141,14 @@ StructTypeDescr::fieldIndex(jsid id, size_t *out)
 }
 
 JSAtom &
-StructTypeDescr::fieldName(size_t index)
+StructTypeDescr::fieldName(size_t index) const
 {
     JSObject &fieldNames = getReservedSlot(JS_DESCR_SLOT_STRUCT_FIELD_NAMES).toObject();
     return fieldNames.getDenseElement(index).toString()->asAtom();
 }
 
 int32_t
-StructTypeDescr::fieldOffset(size_t index)
+StructTypeDescr::fieldOffset(size_t index) const
 {
     JSObject &fieldOffsets =
         getReservedSlot(JS_DESCR_SLOT_STRUCT_FIELD_OFFSETS).toObject();
@@ -1157,7 +1157,7 @@ StructTypeDescr::fieldOffset(size_t index)
 }
 
 SizedTypeDescr&
-StructTypeDescr::fieldDescr(size_t index)
+StructTypeDescr::fieldDescr(size_t index) const
 {
     JSObject &fieldDescrs =
         getReservedSlot(JS_DESCR_SLOT_STRUCT_FIELD_TYPES).toObject();
@@ -1513,16 +1513,16 @@ static int32_t
 TypedObjLengthFromType(TypeDescr &descr)
 {
     switch (descr.kind()) {
-      case TypeDescr::Scalar:
-      case TypeDescr::Reference:
-      case TypeDescr::Struct:
-      case TypeDescr::X4:
+      case type::Scalar:
+      case type::Reference:
+      case type::Struct:
+      case type::X4:
         return 0;
 
-      case TypeDescr::SizedArray:
+      case type::SizedArray:
         return descr.as<SizedArrayTypeDescr>().length();
 
-      case TypeDescr::UnsizedArray:
+      case type::UnsizedArray:
         MOZ_ASSUME_UNREACHABLE("TypedObjLengthFromType() invoked on unsized type");
     }
     MOZ_ASSUME_UNREACHABLE("Invalid kind");
@@ -1562,11 +1562,11 @@ TypedObject::createZeroed(JSContext *cx,
     // Allocate and initialize the memory for this instance.
     // Also initialize the JS_TYPEDOBJ_SLOT_LENGTH slot.
     switch (descr->kind()) {
-      case TypeDescr::Scalar:
-      case TypeDescr::Reference:
-      case TypeDescr::Struct:
-      case TypeDescr::X4:
-      case TypeDescr::SizedArray:
+      case type::Scalar:
+      case type::Reference:
+      case type::Struct:
+      case type::X4:
+      case type::SizedArray:
       {
         size_t totalSize = descr->as<SizedTypeDescr>().size();
         Rooted<ArrayBufferObject*> buffer(cx);
@@ -1578,7 +1578,7 @@ TypedObject::createZeroed(JSContext *cx,
         return obj;
       }
 
-      case TypeDescr::UnsizedArray:
+      case type::UnsizedArray:
       {
         Rooted<SizedTypeDescr*> elementTypeRepr(cx);
         elementTypeRepr = &descr->as<UnsizedArrayTypeDescr>().elementType();
@@ -1639,15 +1639,15 @@ TypedObject::obj_trace(JSTracer *trace, JSObject *object)
             return;
 
         switch (descr.kind()) {
-          case TypeDescr::Scalar:
-          case TypeDescr::Reference:
-          case TypeDescr::Struct:
-          case TypeDescr::SizedArray:
-          case TypeDescr::X4:
+          case type::Scalar:
+          case type::Reference:
+          case type::Struct:
+          case type::SizedArray:
+          case type::X4:
             descr.as<SizedTypeDescr>().traceInstances(trace, mem, 1);
             break;
 
-          case TypeDescr::UnsizedArray:
+          case type::UnsizedArray:
             descr.as<UnsizedArrayTypeDescr>().elementType().traceInstances(trace, mem, typedObj.length());
             break;
         }
@@ -1662,13 +1662,13 @@ TypedObject::obj_lookupGeneric(JSContext *cx, HandleObject obj, HandleId id,
 
     Rooted<TypeDescr*> descr(cx, &obj->as<TypedObject>().typeDescr());
     switch (descr->kind()) {
-      case TypeDescr::Scalar:
-      case TypeDescr::Reference:
-      case TypeDescr::X4:
+      case type::Scalar:
+      case type::Reference:
+      case type::X4:
         break;
 
-      case TypeDescr::SizedArray:
-      case TypeDescr::UnsizedArray:
+      case type::SizedArray:
+      case type::UnsizedArray:
       {
         uint32_t index;
         if (js_IdIsIndex(id, &index))
@@ -1682,7 +1682,7 @@ TypedObject::obj_lookupGeneric(JSContext *cx, HandleObject obj, HandleId id,
         break;
       }
 
-      case TypeDescr::Struct:
+      case type::Struct:
       {
         StructTypeDescr &structDescr = descr->as<StructTypeDescr>();
         size_t index;
@@ -1788,15 +1788,15 @@ TypedObject::obj_getGeneric(JSContext *cx, HandleObject obj, HandleObject receiv
     // Handle everything else here:
 
     switch (typedObj->typeDescr().kind()) {
-      case TypeDescr::Scalar:
-      case TypeDescr::Reference:
+      case type::Scalar:
+      case type::Reference:
         break;
 
-      case TypeDescr::X4:
+      case type::X4:
         break;
 
-      case TypeDescr::SizedArray:
-      case TypeDescr::UnsizedArray:
+      case type::SizedArray:
+      case type::UnsizedArray:
         if (JSID_IS_ATOM(id, cx->names().length)) {
             if (typedObj->owner().isNeutered() || !typedObj->typedMem()) { // unattached
                 JS_ReportErrorNumber(
@@ -1810,7 +1810,7 @@ TypedObject::obj_getGeneric(JSContext *cx, HandleObject obj, HandleObject receiv
         }
         break;
 
-      case TypeDescr::Struct: {
+      case type::Struct: {
         Rooted<StructTypeDescr*> descr(cx, &typedObj->typeDescr().as<StructTypeDescr>());
 
         size_t fieldIndex;
@@ -1849,17 +1849,17 @@ TypedObject::obj_getElement(JSContext *cx, HandleObject obj, HandleObject receiv
     Rooted<TypeDescr *> descr(cx, &typedObj->typeDescr());
 
     switch (descr->kind()) {
-      case TypeDescr::Scalar:
-      case TypeDescr::Reference:
-      case TypeDescr::X4:
-      case TypeDescr::Struct:
+      case type::Scalar:
+      case type::Reference:
+      case type::X4:
+      case type::Struct:
         break;
 
-      case TypeDescr::SizedArray:
+      case type::SizedArray:
         return obj_getArrayElement<SizedArrayTypeDescr>(cx, typedObj, descr,
                                                         index, vp);
 
-      case TypeDescr::UnsizedArray:
+      case type::UnsizedArray:
         return obj_getArrayElement<UnsizedArrayTypeDescr>(cx, typedObj, descr,
                                                           index, vp);
     }
@@ -1905,15 +1905,15 @@ TypedObject::obj_setGeneric(JSContext *cx, HandleObject obj, HandleId id,
         return obj_setElement(cx, obj, index, vp, strict);
 
     switch (typedObj->typeDescr().kind()) {
-      case ScalarTypeDescr::Scalar:
-      case TypeDescr::Reference:
+      case type::Scalar:
+      case type::Reference:
         break;
 
-      case ScalarTypeDescr::X4:
+      case type::X4:
         break;
 
-      case ScalarTypeDescr::SizedArray:
-      case ScalarTypeDescr::UnsizedArray:
+      case type::SizedArray:
+      case type::UnsizedArray:
         if (JSID_IS_ATOM(id, cx->names().length)) {
             JS_ReportErrorNumber(cx, js_GetErrorMessage,
                                  nullptr, JSMSG_CANT_REDEFINE_ARRAY_LENGTH);
@@ -1921,7 +1921,7 @@ TypedObject::obj_setGeneric(JSContext *cx, HandleObject obj, HandleId id,
         }
         break;
 
-      case ScalarTypeDescr::Struct: {
+      case type::Struct: {
         Rooted<StructTypeDescr*> descr(cx, &typedObj->typeDescr().as<StructTypeDescr>());
 
         size_t fieldIndex;
@@ -1955,16 +1955,16 @@ TypedObject::obj_setElement(JSContext *cx, HandleObject obj, uint32_t index,
     Rooted<TypeDescr *> descr(cx, &typedObj->typeDescr());
 
     switch (descr->kind()) {
-      case TypeDescr::Scalar:
-      case TypeDescr::Reference:
-      case TypeDescr::X4:
-      case TypeDescr::Struct:
+      case type::Scalar:
+      case type::Reference:
+      case type::X4:
+      case type::Struct:
         break;
 
-      case TypeDescr::SizedArray:
+      case type::SizedArray:
         return obj_setArrayElement<SizedArrayTypeDescr>(cx, typedObj, descr, index, vp);
 
-      case TypeDescr::UnsizedArray:
+      case type::UnsizedArray:
         return obj_setArrayElement<UnsizedArrayTypeDescr>(cx, typedObj, descr, index, vp);
     }
 
@@ -2000,15 +2000,15 @@ TypedObject::obj_getGenericAttributes(JSContext *cx, HandleObject obj,
     uint32_t index;
     Rooted<TypedObject *> typedObj(cx, &obj->as<TypedObject>());
     switch (typedObj->typeDescr().kind()) {
-      case TypeDescr::Scalar:
-      case TypeDescr::Reference:
+      case type::Scalar:
+      case type::Reference:
         break;
 
-      case TypeDescr::X4:
+      case type::X4:
         break;
 
-      case TypeDescr::SizedArray:
-      case TypeDescr::UnsizedArray:
+      case type::SizedArray:
+      case type::UnsizedArray:
         if (js_IdIsIndex(id, &index)) {
             *attrsp = JSPROP_ENUMERATE | JSPROP_PERMANENT;
             return true;
@@ -2019,7 +2019,7 @@ TypedObject::obj_getGenericAttributes(JSContext *cx, HandleObject obj,
         }
         break;
 
-      case TypeDescr::Struct:
+      case type::Struct:
         size_t index;
         if (typedObj->typeDescr().as<StructTypeDescr>().fieldIndex(id, &index)) {
             *attrsp = JSPROP_ENUMERATE | JSPROP_PERMANENT;
@@ -2043,16 +2043,16 @@ IsOwnId(JSContext *cx, HandleObject obj, HandleId id)
     uint32_t index;
     Rooted<TypedObject *> typedObj(cx, &obj->as<TypedObject>());
     switch (typedObj->typeDescr().kind()) {
-      case TypeDescr::Scalar:
-      case TypeDescr::Reference:
-      case TypeDescr::X4:
+      case type::Scalar:
+      case type::Reference:
+      case type::X4:
         return false;
 
-      case TypeDescr::SizedArray:
-      case TypeDescr::UnsizedArray:
+      case type::SizedArray:
+      case type::UnsizedArray:
         return js_IdIsIndex(id, &index) || JSID_IS_ATOM(id, cx->names().length);
 
-      case TypeDescr::Struct:
+      case type::Struct:
         size_t index;
         if (typedObj->typeDescr().as<StructTypeDescr>().fieldIndex(id, &index))
             return true;
@@ -2102,9 +2102,9 @@ TypedObject::obj_enumerate(JSContext *cx, HandleObject obj, JSIterateOp enum_op,
     Rooted<TypedObject *> typedObj(cx, &obj->as<TypedObject>());
     Rooted<TypeDescr *> descr(cx, &typedObj->typeDescr());
     switch (descr->kind()) {
-      case TypeDescr::Scalar:
-      case TypeDescr::Reference:
-      case TypeDescr::X4:
+      case type::Scalar:
+      case type::Reference:
+      case type::X4:
         switch (enum_op) {
           case JSENUMERATE_INIT_ALL:
           case JSENUMERATE_INIT:
@@ -2118,8 +2118,8 @@ TypedObject::obj_enumerate(JSContext *cx, HandleObject obj, JSIterateOp enum_op,
         }
         break;
 
-      case TypeDescr::SizedArray:
-      case TypeDescr::UnsizedArray:
+      case type::SizedArray:
+      case type::UnsizedArray:
         switch (enum_op) {
           case JSENUMERATE_INIT_ALL:
           case JSENUMERATE_INIT:
@@ -2146,7 +2146,7 @@ TypedObject::obj_enumerate(JSContext *cx, HandleObject obj, JSIterateOp enum_op,
         }
         break;
 
-      case TypeDescr::Struct:
+      case type::Struct:
         switch (enum_op) {
           case JSENUMERATE_INIT_ALL:
           case JSENUMERATE_INIT:
@@ -2262,16 +2262,16 @@ static int32_t
 LengthForType(TypeDescr &descr)
 {
     switch (descr.kind()) {
-      case TypeDescr::Scalar:
-      case TypeDescr::Reference:
-      case TypeDescr::Struct:
-      case TypeDescr::X4:
+      case type::Scalar:
+      case type::Reference:
+      case type::Struct:
+      case type::X4:
         return 0;
 
-      case TypeDescr::SizedArray:
+      case type::SizedArray:
         return descr.as<SizedArrayTypeDescr>().length();
 
-      case TypeDescr::UnsizedArray:
+      case type::UnsizedArray:
         return 0;
     }
 
@@ -3080,15 +3080,15 @@ visitReferences(SizedTypeDescr &descr,
         return;
 
     switch (descr.kind()) {
-      case TypeDescr::Scalar:
-      case TypeDescr::X4:
+      case type::Scalar:
+      case type::X4:
         return;
 
-      case TypeDescr::Reference:
+      case type::Reference:
         visitor.visitReference(descr.as<ReferenceTypeDescr>(), mem);
         return;
 
-      case TypeDescr::SizedArray:
+      case type::SizedArray:
       {
         SizedArrayTypeDescr &arrayDescr = descr.as<SizedArrayTypeDescr>();
         SizedTypeDescr &elementDescr = arrayDescr.elementType();
@@ -3099,12 +3099,12 @@ visitReferences(SizedTypeDescr &descr,
         return;
       }
 
-      case TypeDescr::UnsizedArray:
+      case type::UnsizedArray:
       {
         MOZ_ASSUME_UNREACHABLE("Only Sized Type representations");
       }
 
-      case TypeDescr::Struct:
+      case type::Struct:
       {
         StructTypeDescr &structDescr = descr.as<StructTypeDescr>();
         for (size_t i = 0; i < structDescr.fieldCount(); i++) {
diff --git a/js/src/builtin/TypedObject.h b/js/src/builtin/TypedObject.h
index e7f76810e5ef..e02db2527d29 100644
--- a/js/src/builtin/TypedObject.h
+++ b/js/src/builtin/TypedObject.h
@@ -126,6 +126,33 @@ static T ConvertScalar(double d)
     }
 }
 
+namespace type {
+
+enum Kind {
+    Scalar = JS_TYPEREPR_SCALAR_KIND,
+    Reference = JS_TYPEREPR_REFERENCE_KIND,
+    X4 = JS_TYPEREPR_X4_KIND,
+    Struct = JS_TYPEREPR_STRUCT_KIND,
+    SizedArray = JS_TYPEREPR_SIZED_ARRAY_KIND,
+    UnsizedArray = JS_TYPEREPR_UNSIZED_ARRAY_KIND,
+};
+
+static inline bool isSized(type::Kind kind) {
+    return kind > JS_TYPEREPR_MAX_UNSIZED_KIND;
+}
+
+}
+
+///////////////////////////////////////////////////////////////////////////
+// Typed Prototypes
+
+class SizedTypeDescr;
+class SimpleTypeDescr;
+class ComplexTypeDescr;
+class X4TypeDescr;
+class StructTypeDescr;
+class SizedTypedProto;
+
 /*
  * The prototype for a typed object. Currently, carries a link to the
  * type descriptor. Eventually will carry most of the type information
@@ -154,25 +181,21 @@ class TypeDescr : public JSObject
     // fun and rejoicing.
     static const Class class_;
 
-    enum Kind {
-        Scalar = JS_TYPEREPR_SCALAR_KIND,
-        Reference = JS_TYPEREPR_REFERENCE_KIND,
-        X4 = JS_TYPEREPR_X4_KIND,
-        Struct = JS_TYPEREPR_STRUCT_KIND,
-        SizedArray = JS_TYPEREPR_SIZED_ARRAY_KIND,
-        UnsizedArray = JS_TYPEREPR_UNSIZED_ARRAY_KIND,
-    };
-
-    static bool isSized(Kind kind) {
+  public:
+    static bool isSized(type::Kind kind) {
         return kind > JS_TYPEREPR_MAX_UNSIZED_KIND;
     }
 
+    TypedProto &typedProto() const {
+        return getReservedSlot(JS_DESCR_SLOT_TYPROTO).toObject().as<TypedProto>();
+    }
+
     JSAtom &stringRepr() const {
         return getReservedSlot(JS_DESCR_SLOT_STRING_REPR).toString()->asAtom();
     }
 
-    TypeDescr::Kind kind() const {
-        return (TypeDescr::Kind) getReservedSlot(JS_DESCR_SLOT_KIND).toInt32();
+    type::Kind kind() const {
+        return (type::Kind) getReservedSlot(JS_DESCR_SLOT_KIND).toInt32();
     }
 
     bool opaque() const {
@@ -183,7 +206,7 @@ class TypeDescr : public JSObject
         return !opaque();
     }
 
-    int32_t alignment() {
+    int32_t alignment() const {
         return getReservedSlot(JS_DESCR_SLOT_ALIGNMENT).toInt32();
     }
 };
@@ -193,7 +216,7 @@ typedef Handle<TypeDescr*> HandleTypeDescr;
 class SizedTypeDescr : public TypeDescr
 {
   public:
-    int32_t size() {
+    int32_t size() const {
         return getReservedSlot(JS_DESCR_SLOT_SIZE).toInt32();
     }
 
@@ -233,7 +256,7 @@ class ScalarTypeDescr : public SimpleTypeDescr
     };
     static const int32_t TYPE_MAX = TYPE_UINT8_CLAMPED + 1;
 
-    static const TypeDescr::Kind Kind = TypeDescr::Scalar;
+    static const type::Kind Kind = type::Scalar;
     static const bool Opaque = false;
     static int32_t size(Type t);
     static int32_t alignment(Type t);
@@ -282,7 +305,7 @@ class ReferenceTypeDescr : public SimpleTypeDescr
     static const int32_t TYPE_MAX = TYPE_STRING + 1;
     static const char *typeName(Type type);
 
-    static const TypeDescr::Kind Kind = TypeDescr::Reference;
+    static const type::Kind Kind = type::Reference;
     static const bool Opaque = true;
     static const Class class_;
     static int32_t size(Type t);
@@ -328,7 +351,7 @@ class X4TypeDescr : public ComplexTypeDescr
         TYPE_FLOAT32 = JS_X4TYPEREPR_FLOAT32,
     };
 
-    static const TypeDescr::Kind Kind = TypeDescr::X4;
+    static const type::Kind Kind = type::X4;
     static const bool Opaque = false;
     static const Class class_;
     static int32_t size(Type t);
@@ -407,13 +430,13 @@ class UnsizedArrayTypeDescr : public TypeDescr
 {
   public:
     static const Class class_;
-    static const TypeDescr::Kind Kind = TypeDescr::UnsizedArray;
+    static const type::Kind Kind = type::UnsizedArray;
 
     // This is the sized method on unsized array type objects.  It
     // produces a sized variant.
     static bool dimension(JSContext *cx, unsigned int argc, jsval *vp);
 
-    SizedTypeDescr &elementType() {
+    SizedTypeDescr &elementType() const {
         return getReservedSlot(JS_DESCR_SLOT_ARRAY_ELEM_TYPE).toObject().as<SizedTypeDescr>();
     }
 };
@@ -425,13 +448,13 @@ class SizedArrayTypeDescr : public ComplexTypeDescr
 {
   public:
     static const Class class_;
-    static const TypeDescr::Kind Kind = TypeDescr::SizedArray;
+    static const type::Kind Kind = type::SizedArray;
 
-    SizedTypeDescr &elementType() {
+    SizedTypeDescr &elementType() const {
         return getReservedSlot(JS_DESCR_SLOT_ARRAY_ELEM_TYPE).toObject().as<SizedTypeDescr>();
     }
 
-    int32_t length() {
+    int32_t length() const {
         return getReservedSlot(JS_DESCR_SLOT_SIZED_ARRAY_LENGTH).toInt32();
     }
 };
@@ -469,20 +492,20 @@ class StructTypeDescr : public ComplexTypeDescr
     static const Class class_;
 
     // Returns the number of fields defined in this struct.
-    size_t fieldCount();
+    size_t fieldCount() const;
 
     // Set `*out` to the index of the field named `id` and returns true,
     // or return false if no such field exists.
-    bool fieldIndex(jsid id, size_t *out);
+    bool fieldIndex(jsid id, size_t *out) const;
 
     // Return the name of the field at index `index`.
-    JSAtom &fieldName(size_t index);
+    JSAtom &fieldName(size_t index) const;
 
     // Return the type descr of the field at index `index`.
-    SizedTypeDescr &fieldDescr(size_t index);
+    SizedTypeDescr &fieldDescr(size_t index) const;
 
     // Return the offset of the field at index `index`.
-    int32_t fieldOffset(size_t index);
+    int32_t fieldOffset(size_t index) const;
 };
 
 typedef Handle<StructTypeDescr*> HandleStructTypeDescr;
@@ -670,14 +693,14 @@ class TypedObject : public ArrayBufferViewObject
 
     int32_t size() const {
         switch (typeDescr().kind()) {
-          case TypeDescr::Scalar:
-          case TypeDescr::X4:
-          case TypeDescr::Reference:
-          case TypeDescr::Struct:
-          case TypeDescr::SizedArray:
+          case type::Scalar:
+          case type::X4:
+          case type::Reference:
+          case type::Struct:
+          case type::SizedArray:
             return typeDescr().as<SizedTypeDescr>().size();
 
-          case TypeDescr::UnsizedArray: {
+          case type::UnsizedArray: {
             SizedTypeDescr &elementType = typeDescr().as<UnsizedArrayTypeDescr>().elementType();
             return elementType.size() * length();
           }
diff --git a/js/src/jit/IonBuilder.cpp b/js/src/jit/IonBuilder.cpp
index b4327b9b5423..fe45c436bba7 100644
--- a/js/src/jit/IonBuilder.cpp
+++ b/js/src/jit/IonBuilder.cpp
@@ -6770,19 +6770,19 @@ IonBuilder::getElemTryTypedObject(bool *emitted, MDefinition *obj, MDefinition *
         return true;
 
     switch (elemDescrs.kind()) {
-      case TypeDescr::X4:
+      case type::X4:
         // FIXME (bug 894105): load into a MIRType_float32x4 etc
         return true;
 
-      case TypeDescr::Struct:
-      case TypeDescr::SizedArray:
+      case type::Struct:
+      case type::SizedArray:
         return getElemTryComplexElemOfTypedObject(emitted,
                                                   obj,
                                                   index,
                                                   objDescrs,
                                                   elemDescrs,
                                                   elemSize);
-      case TypeDescr::Scalar:
+      case type::Scalar:
         return getElemTryScalarElemOfTypedObject(emitted,
                                                  obj,
                                                  index,
@@ -6790,10 +6790,10 @@ IonBuilder::getElemTryTypedObject(bool *emitted, MDefinition *obj, MDefinition *
                                                  elemDescrs,
                                                  elemSize);
 
-      case TypeDescr::Reference:
+      case type::Reference:
         return true;
 
-      case TypeDescr::UnsizedArray:
+      case type::UnsizedArray:
         MOZ_ASSUME_UNREACHABLE("Unsized arrays cannot be element types");
     }
 
@@ -7683,18 +7683,18 @@ IonBuilder::setElemTryTypedObject(bool *emitted, MDefinition *obj,
         return true;
 
     switch (elemTypeDescrs.kind()) {
-      case TypeDescr::X4:
+      case type::X4:
         // FIXME (bug 894105): store a MIRType_float32x4 etc
         return true;
 
-      case TypeDescr::Reference:
-      case TypeDescr::Struct:
-      case TypeDescr::SizedArray:
-      case TypeDescr::UnsizedArray:
+      case type::Reference:
+      case type::Struct:
+      case type::SizedArray:
+      case type::UnsizedArray:
         // For now, only optimize storing scalars.
         return true;
 
-      case TypeDescr::Scalar:
+      case type::Scalar:
         return setElemTryScalarElemOfTypedObject(emitted,
                                                  obj,
                                                  index,
@@ -8708,15 +8708,15 @@ IonBuilder::getPropTryTypedObject(bool *emitted, MDefinition *obj, PropertyName
         return true;
 
     switch (fieldDescrs.kind()) {
-      case TypeDescr::Reference:
+      case type::Reference:
         return true;
 
-      case TypeDescr::X4:
+      case type::X4:
         // FIXME (bug 894104): load into a MIRType_float32x4 etc
         return true;
 
-      case TypeDescr::Struct:
-      case TypeDescr::SizedArray:
+      case type::Struct:
+      case type::SizedArray:
         return getPropTryComplexPropOfTypedObject(emitted,
                                                   obj,
                                                   fieldOffset,
@@ -8724,14 +8724,14 @@ IonBuilder::getPropTryTypedObject(bool *emitted, MDefinition *obj, PropertyName
                                                   fieldIndex,
                                                   resultTypes);
 
-      case TypeDescr::Scalar:
+      case type::Scalar:
         return getPropTryScalarPropOfTypedObject(emitted,
                                                  obj,
                                                  fieldOffset,
                                                  fieldDescrs,
                                                  resultTypes);
 
-      case TypeDescr::UnsizedArray:
+      case type::UnsizedArray:
         MOZ_ASSUME_UNREACHABLE("Field of unsized array type");
     }
 
@@ -9362,18 +9362,18 @@ IonBuilder::setPropTryTypedObject(bool *emitted, MDefinition *obj,
         return true;
 
     switch (fieldDescrs.kind()) {
-      case TypeDescr::X4:
+      case type::X4:
         // FIXME (bug 894104): store into a MIRType_float32x4 etc
         return true;
 
-      case TypeDescr::Reference:
-      case TypeDescr::Struct:
-      case TypeDescr::SizedArray:
-      case TypeDescr::UnsizedArray:
+      case type::Reference:
+      case type::Struct:
+      case type::SizedArray:
+      case type::UnsizedArray:
         // For now, only optimize storing scalars.
         return true;
 
-      case TypeDescr::Scalar:
+      case type::Scalar:
         return setPropTryScalarPropOfTypedObject(emitted, obj, fieldOffset,
                                                  value, fieldDescrs);
     }
@@ -10402,7 +10402,7 @@ IonBuilder::lookupTypedObjectField(MDefinition *typedObj,
         return false;
 
     // Must be accessing a struct.
-    if (!objDescrs.allOfKind(TypeDescr::Struct))
+    if (!objDescrs.allOfKind(type::Struct))
         return true;
 
     // Determine the type/offset of the field `name`, if any.
diff --git a/js/src/jit/MCallOptimize.cpp b/js/src/jit/MCallOptimize.cpp
index 42f0328c4e5b..4f5f0631ac53 100644
--- a/js/src/jit/MCallOptimize.cpp
+++ b/js/src/jit/MCallOptimize.cpp
@@ -1460,7 +1460,7 @@ IonBuilder::elementAccessIsTypedObjectArrayOfScalarType(MDefinition* obj, MDefin
     if (!objDescrs.arrayElementType(*this, &elemDescrs))
         return false;
 
-    if (elemDescrs.empty() || elemDescrs.kind() != TypeDescr::Scalar)
+    if (elemDescrs.empty() || elemDescrs.kind() != type::Scalar)
         return false;
 
     JS_ASSERT(TypeDescr::isSized(elemDescrs.kind()));
diff --git a/js/src/jit/TypeDescrSet.cpp b/js/src/jit/TypeDescrSet.cpp
index 9c787f16c8b1..5335a627a5b9 100644
--- a/js/src/jit/TypeDescrSet.cpp
+++ b/js/src/jit/TypeDescrSet.cpp
@@ -176,14 +176,14 @@ TypeDescrSet::allOfArrayKind()
         return false;
 
     switch (kind()) {
-      case TypeDescr::SizedArray:
-      case TypeDescr::UnsizedArray:
+      case type::SizedArray:
+      case type::UnsizedArray:
         return true;
 
-      case TypeDescr::X4:
-      case TypeDescr::Reference:
-      case TypeDescr::Scalar:
-      case TypeDescr::Struct:
+      case type::X4:
+      case type::Reference:
+      case type::Scalar:
+      case type::Struct:
         return false;
     }
 
@@ -191,7 +191,7 @@ TypeDescrSet::allOfArrayKind()
 }
 
 bool
-TypeDescrSet::allOfKind(TypeDescr::Kind aKind)
+TypeDescrSet::allOfKind(type::Kind aKind)
 {
     if (empty())
         return false;
@@ -226,7 +226,7 @@ TypeDescrSet::knownPrototype() const
     return &get(0)->as<ComplexTypeDescr>().instancePrototype();
 }
 
-TypeDescr::Kind
+type::Kind
 TypeDescrSet::kind()
 {
     JS_ASSERT(!empty());
@@ -237,7 +237,7 @@ template<typename T>
 bool
 TypeDescrSet::genericType(typename T::Type *out)
 {
-    JS_ASSERT(allOfKind(TypeDescr::Scalar));
+    JS_ASSERT(allOfKind(type::Scalar));
 
     typename T::Type type = get(0)->as<T>().type();
     for (size_t i = 1; i < length(); i++) {
@@ -271,10 +271,10 @@ bool
 TypeDescrSet::hasKnownArrayLength(int32_t *l)
 {
     switch (kind()) {
-      case TypeDescr::UnsizedArray:
+      case type::UnsizedArray:
         return false;
 
-      case TypeDescr::SizedArray:
+      case type::SizedArray:
       {
         const size_t result = get(0)->as<SizedArrayTypeDescr>().length();
         for (size_t i = 1; i < length(); i++) {
@@ -297,12 +297,12 @@ TypeDescrSet::arrayElementType(IonBuilder &builder, TypeDescrSet *out)
     TypeDescrSetBuilder elementTypes;
     for (size_t i = 0; i < length(); i++) {
         switch (kind()) {
-          case TypeDescr::UnsizedArray:
+          case type::UnsizedArray:
             if (!elementTypes.insert(&get(i)->as<UnsizedArrayTypeDescr>().elementType()))
                 return false;
             break;
 
-          case TypeDescr::SizedArray:
+          case type::SizedArray:
             if (!elementTypes.insert(&get(i)->as<SizedArrayTypeDescr>().elementType()))
                 return false;
             break;
@@ -321,7 +321,7 @@ TypeDescrSet::fieldNamed(IonBuilder &builder,
                          TypeDescrSet *out,
                          size_t *index)
 {
-    JS_ASSERT(kind() == TypeDescr::Struct);
+    JS_ASSERT(kind() == type::Struct);
 
     // Initialize `*offset` and `*out` for the case where incompatible
     // or absent fields are found.
diff --git a/js/src/jit/TypeDescrSet.h b/js/src/jit/TypeDescrSet.h
index 8ef0a7079d84..1ca256a446e6 100644
--- a/js/src/jit/TypeDescrSet.h
+++ b/js/src/jit/TypeDescrSet.h
@@ -86,7 +86,7 @@ class TypeDescrSet {
     // Query the set
 
     bool empty() const;
-    bool allOfKind(TypeDescr::Kind kind);
+    bool allOfKind(type::Kind kind);
 
     // Returns true only when non-empty and `kind()` is
     // `TypeDescr::Array`
@@ -108,7 +108,7 @@ class TypeDescrSet {
     //////////////////////////////////////////////////////////////////////
     // The following operations are only valid on a non-empty set:
 
-    TypeDescr::Kind kind();
+    type::Kind kind();
 
     // Returns the prototype that a typed object whose type is within
     // this TypeDescrSet would have. Returns `null` if this cannot be
@@ -118,7 +118,7 @@ class TypeDescrSet {
     //////////////////////////////////////////////////////////////////////
     // Scalar operations
     //
-    // Only valid when `kind() == TypeDescr::Scalar`
+    // Only valid when `kind() == type::Scalar`
 
     // If all type descrs in this set have a single type, returns true
     // and sets *out. Else returns false.
@@ -127,7 +127,7 @@ class TypeDescrSet {
     //////////////////////////////////////////////////////////////////////
     // Reference operations
     //
-    // Only valid when `kind() == TypeDescr::Reference`
+    // Only valid when `kind() == type::Reference`
 
     // If all type descrs in this set have a single type, returns true
     // and sets *out. Else returns false.
@@ -136,7 +136,7 @@ class TypeDescrSet {
     //////////////////////////////////////////////////////////////////////
     // Reference operations
     //
-    // Only valid when `kind() == TypeDescr::X4`
+    // Only valid when `kind() == type::X4`
 
     // If all type descrs in this set have a single type, returns true
     // and sets *out. Else returns false.
@@ -145,7 +145,7 @@ class TypeDescrSet {
     //////////////////////////////////////////////////////////////////////
     // SizedArray operations
     //
-    // Only valid when `kind() == TypeDescr::SizedArray`
+    // Only valid when `kind() == type::SizedArray`
 
     // Determines whether all arrays in this set have the same,
     // statically known, array length and return that length
@@ -160,7 +160,7 @@ class TypeDescrSet {
     //////////////////////////////////////////////////////////////////////
     // Struct operations
     //
-    // Only valid when `kind() == TypeDescr::Struct`
+    // Only valid when `kind() == type::Struct`
 
     // Searches the type in the set for a field named `id`. All
     // possible types must agree on the offset of the field within the