diff --git a/js/public/WeakMapPtr.h b/js/public/WeakMapPtr.h
new file mode 100644
index 000000000000..ffebd7a213e7
--- /dev/null
+++ b/js/public/WeakMapPtr.h
@@ -0,0 +1,46 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef js_WeakMapPtr_h
+#define js_WeakMapPtr_h
+
+#include "jspubtd.h"
+
+#include "js/TypeDecls.h"
+
+namespace JS {
+
+// A wrapper around the internal C++ representation of SpiderMonkey WeakMaps,
+// usable outside the engine.
+//
+// The supported template specializations are enumerated in WeakMapPtr.cpp. If
+// you want to use this class for a different key/value combination, add it to
+// the list and the compiler will generate the relevant machinery.
+template <typename K, typename V>
+class JS_PUBLIC_API(WeakMapPtr)
+{
+  public:
+    WeakMapPtr() : ptr(nullptr) {};
+    bool init(JSContext *cx);
+    bool initialized() { return ptr != nullptr; };
+    void destroy();
+    virtual ~WeakMapPtr() { MOZ_ASSERT(!initialized()); }
+    void trace(JSTracer *tracer);
+
+    V lookup(const K &key);
+    bool put(const K &key, const V &value);
+
+  private:
+    void *ptr;
+
+    // WeakMapPtr is neither copyable nor assignable.
+    WeakMapPtr(const WeakMapPtr &wmp) MOZ_DELETE;
+    WeakMapPtr &operator=(const WeakMapPtr &wmp) MOZ_DELETE;
+};
+
+} /* namespace JS */
+
+#endif  /* js_WeakMapPtr_h */
diff --git a/js/src/jsapi-tests/testIntTypesABI.cpp b/js/src/jsapi-tests/testIntTypesABI.cpp
index ca851018bfb7..d2d9afc2d42b 100644
--- a/js/src/jsapi-tests/testIntTypesABI.cpp
+++ b/js/src/jsapi-tests/testIntTypesABI.cpp
@@ -37,6 +37,7 @@
 #include "js/Utility.h"
 #include "js/Value.h"
 #include "js/Vector.h"
+#include "js/WeakMapPtr.h"
 #include "jsapi-tests/tests.h"
 
 /*
diff --git a/js/src/jsweakmap.h b/js/src/jsweakmap.h
index 4b4c829beeed..804614ec3d43 100644
--- a/js/src/jsweakmap.h
+++ b/js/src/jsweakmap.h
@@ -85,7 +85,8 @@ class WeakMapBase {
     // Trace all delayed weak map bindings. Used by the cycle collector.
     static void traceAllMappings(WeakMapTracer *tracer);
 
-    void check() { JS_ASSERT(next == WeakMapNotInList); }
+    bool isInList() { return next != WeakMapNotInList; }
+    void check() { JS_ASSERT(!isInList()); }
 
     // Remove everything from the weak map list for a compartment.
     static void resetCompartmentWeakMapList(JSCompartment *c);
diff --git a/js/src/moz.build b/js/src/moz.build
index 9ddfca91ab66..c75c58294402 100644
--- a/js/src/moz.build
+++ b/js/src/moz.build
@@ -88,6 +88,7 @@ EXPORTS.js += [
     '../public/Utility.h',
     '../public/Value.h',
     '../public/Vector.h',
+    '../public/WeakMapPtr.h',
 ]
 
 UNIFIED_SOURCES += [
@@ -189,6 +190,7 @@ UNIFIED_SOURCES += [
     'vm/TypedArrayObject.cpp',
     'vm/Unicode.cpp',
     'vm/Value.cpp',
+    'vm/WeakMapPtr.cpp',
     'vm/Xdr.cpp',
     'yarr/PageBlock.cpp',
     'yarr/YarrCanonicalizeUCS2.cpp',
diff --git a/js/src/vm/WeakMapPtr.cpp b/js/src/vm/WeakMapPtr.cpp
new file mode 100644
index 000000000000..3b905a98db2e
--- /dev/null
+++ b/js/src/vm/WeakMapPtr.cpp
@@ -0,0 +1,114 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "js/WeakMapPtr.h"
+
+#include "jsweakmap.h"
+
+//
+// Machinery for the externally-linkable JS::WeakMapPtr, which wraps js::WeakMap
+// for a few public data types.
+//
+
+using namespace js;
+
+namespace {
+
+template<typename T>
+struct DataType
+{
+};
+
+template<>
+struct DataType<JSObject*>
+{
+    typedef EncapsulatedPtrObject Encapsulated;
+    static JSObject *NullValue() { return nullptr; }
+};
+
+template<>
+struct DataType<JS::Value>
+{
+    typedef EncapsulatedValue Encapsulated;
+    static JS::Value NullValue() { return JS::UndefinedValue(); }
+};
+
+template <typename K, typename V>
+struct Utils
+{
+    typedef typename DataType<K>::Encapsulated KeyType;
+    typedef typename DataType<V>::Encapsulated ValueType;
+    typedef WeakMap<KeyType, ValueType> Type;
+    typedef Type* PtrType;
+    static PtrType cast(void *ptr) { return static_cast<PtrType>(ptr); }
+};
+
+} /* namespace */
+
+template <typename K, typename V>
+void
+JS::WeakMapPtr<K, V>::destroy()
+{
+    MOZ_ASSERT(initialized());
+    auto map = Utils<K, V>::cast(ptr);
+    // If this destruction happens mid-GC, we might be in the compartment's list
+    // of known live weakmaps. If we are, remove ourselves before deleting.
+    if (map->isInList())
+        WeakMapBase::removeWeakMapFromList(map);
+    map->check();
+    js_delete(map);
+    ptr = nullptr;
+}
+
+template <typename K, typename V>
+bool
+JS::WeakMapPtr<K, V>::init(JSContext *cx)
+{
+    MOZ_ASSERT(!initialized());
+    typename Utils<K, V>::PtrType map = cx->runtime()->new_<typename Utils<K,V>::Type>(cx);
+    if (!map || !map->init())
+        return false;
+    ptr = map;
+    return true;
+}
+
+template <typename K, typename V>
+void
+JS::WeakMapPtr<K, V>::trace(JSTracer *trc)
+{
+    MOZ_ASSERT(initialized());
+    return Utils<K, V>::cast(ptr)->trace(trc);
+}
+
+template <typename K, typename V>
+V
+JS::WeakMapPtr<K, V>::lookup(const K &key)
+{
+    MOZ_ASSERT(initialized());
+    typename Utils<K, V>::Type::Ptr result = Utils<K, V>::cast(ptr)->lookup(key);
+    if (!result)
+        return DataType<V>::NullValue();
+    return result->value();
+}
+
+template <typename K, typename V>
+bool
+JS::WeakMapPtr<K, V>::put(const K &key, const V &value)
+{
+    MOZ_ASSERT(initialized());
+    return Utils<K, V>::cast(ptr)->put(key, value);
+}
+
+//
+// Supported specializations of JS::WeakMap:
+//
+
+template class JS::WeakMapPtr<JSObject*, JSObject*>;
+
+#ifdef DEBUG
+// Nobody's using this at the moment, but we want to make sure it compiles.
+template class JS::WeakMapPtr<JSObject*, JS::Value>;
+#endif