diff --git a/Userland/Libraries/LibJS/CMakeLists.txt b/Userland/Libraries/LibJS/CMakeLists.txt
index 1f8b0684dab..e59cc737fa1 100644
--- a/Userland/Libraries/LibJS/CMakeLists.txt
+++ b/Userland/Libraries/LibJS/CMakeLists.txt
@@ -20,6 +20,7 @@ set(SOURCES
     Heap/Handle.cpp
     Heap/Heap.cpp
     Heap/HeapBlock.cpp
+    Heap/MarkedVector.cpp
     Interpreter.cpp
     Lexer.cpp
     MarkupGenerator.cpp
diff --git a/Userland/Libraries/LibJS/Forward.h b/Userland/Libraries/LibJS/Forward.h
index 9ed9134cb80..e67045445c6 100644
--- a/Userland/Libraries/LibJS/Forward.h
+++ b/Userland/Libraries/LibJS/Forward.h
@@ -228,6 +228,9 @@ class ThrowCompletionOr;
 template<class T>
 class Handle;
 
+template<class T>
+class MarkedVector;
+
 namespace Bytecode {
 class BasicBlock;
 struct Executable;
diff --git a/Userland/Libraries/LibJS/Heap/Heap.cpp b/Userland/Libraries/LibJS/Heap/Heap.cpp
index e616ecbb986..3e075cb2e46 100644
--- a/Userland/Libraries/LibJS/Heap/Heap.cpp
+++ b/Userland/Libraries/LibJS/Heap/Heap.cpp
@@ -119,6 +119,11 @@ void Heap::gather_roots(HashTable<Cell*>& roots)
         }
     }
 
+    for (auto& vector : m_marked_vectors) {
+        for (auto* cell : vector.cells())
+            roots.set(cell);
+    }
+
     if constexpr (HEAP_DEBUG) {
         dbgln("gather_roots:");
         for (auto* root : roots)
@@ -318,6 +323,18 @@ void Heap::did_destroy_marked_value_list(Badge<MarkedValueList>, MarkedValueList
     m_marked_value_lists.remove(list);
 }
 
+void Heap::did_create_marked_vector(Badge<MarkedVectorBase>, MarkedVectorBase& vector)
+{
+    VERIFY(!m_marked_vectors.contains(vector));
+    m_marked_vectors.append(vector);
+}
+
+void Heap::did_destroy_marked_vector(Badge<MarkedVectorBase>, MarkedVectorBase& vector)
+{
+    VERIFY(m_marked_vectors.contains(vector));
+    m_marked_vectors.remove(vector);
+}
+
 void Heap::did_create_weak_container(Badge<WeakContainer>, WeakContainer& set)
 {
     VERIFY(!m_weak_containers.contains(set));
diff --git a/Userland/Libraries/LibJS/Heap/Heap.h b/Userland/Libraries/LibJS/Heap/Heap.h
index a68e3ffc5bd..6b2deb7335d 100644
--- a/Userland/Libraries/LibJS/Heap/Heap.h
+++ b/Userland/Libraries/LibJS/Heap/Heap.h
@@ -19,6 +19,7 @@
 #include <LibJS/Heap/Cell.h>
 #include <LibJS/Heap/CellAllocator.h>
 #include <LibJS/Heap/Handle.h>
+#include <LibJS/Heap/MarkedVector.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/WeakContainer.h>
 
@@ -75,6 +76,9 @@ public:
     void did_create_marked_value_list(Badge<MarkedValueList>, MarkedValueList&);
     void did_destroy_marked_value_list(Badge<MarkedValueList>, MarkedValueList&);
 
+    void did_create_marked_vector(Badge<MarkedVectorBase>, MarkedVectorBase&);
+    void did_destroy_marked_vector(Badge<MarkedVectorBase>, MarkedVectorBase&);
+
     void did_create_weak_container(Badge<WeakContainer>, WeakContainer&);
     void did_destroy_weak_container(Badge<WeakContainer>, WeakContainer&);
 
@@ -115,6 +119,7 @@ private:
 
     HandleImpl::List m_handles;
 
+    MarkedVectorBase::List m_marked_vectors;
     MarkedValueList::List m_marked_value_lists;
 
     WeakContainer::List m_weak_containers;
diff --git a/Userland/Libraries/LibJS/Heap/MarkedVector.cpp b/Userland/Libraries/LibJS/Heap/MarkedVector.cpp
new file mode 100644
index 00000000000..8400704cca0
--- /dev/null
+++ b/Userland/Libraries/LibJS/Heap/MarkedVector.cpp
@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Heap/Heap.h>
+#include <LibJS/Heap/MarkedVector.h>
+
+namespace JS {
+
+MarkedVectorBase::MarkedVectorBase(Heap& heap)
+    : m_heap(heap)
+{
+    m_heap.did_create_marked_vector({}, *this);
+}
+
+MarkedVectorBase::MarkedVectorBase(MarkedVectorBase&& other)
+    : m_heap(other.m_heap)
+    , m_cells(move(other.m_cells))
+{
+    m_heap.did_create_marked_vector({}, *this);
+}
+
+MarkedVectorBase::~MarkedVectorBase()
+{
+    m_heap.did_destroy_marked_vector({}, *this);
+}
+
+}
diff --git a/Userland/Libraries/LibJS/Heap/MarkedVector.h b/Userland/Libraries/LibJS/Heap/MarkedVector.h
new file mode 100644
index 00000000000..0b353763146
--- /dev/null
+++ b/Userland/Libraries/LibJS/Heap/MarkedVector.h
@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/IntrusiveList.h>
+#include <AK/Noncopyable.h>
+#include <AK/Vector.h>
+#include <LibJS/Forward.h>
+#include <LibJS/Heap/Cell.h>
+
+namespace JS {
+
+class MarkedVectorBase {
+    AK_MAKE_NONCOPYABLE(MarkedVectorBase);
+
+public:
+    void append(Cell* cell) { m_cells.append(cell); }
+    void prepend(Cell* cell) { m_cells.prepend(cell); }
+    size_t size() const { return m_cells.size(); }
+
+    Span<Cell*> cells() { return m_cells.span(); }
+
+protected:
+    explicit MarkedVectorBase(Heap&);
+
+    MarkedVectorBase(MarkedVectorBase&&);
+    MarkedVectorBase& operator=(MarkedVectorBase&& other)
+    {
+        m_cells = move(other.m_cells);
+        return *this;
+    }
+
+    ~MarkedVectorBase();
+
+    Heap& m_heap;
+
+    IntrusiveListNode<MarkedVectorBase> m_list_node;
+    Vector<Cell*> m_cells;
+
+public:
+    using List = IntrusiveList<&MarkedVectorBase::m_list_node>;
+};
+
+template<typename T>
+class MarkedVector : public MarkedVectorBase {
+public:
+    explicit MarkedVector(Heap& heap)
+        : MarkedVectorBase(heap)
+    {
+    }
+
+    ~MarkedVector() = default;
+
+    MarkedVector(MarkedVector&&) = default;
+    MarkedVector& operator=(MarkedVector&&) = default;
+
+    Span<T*> span() { return Span<T*> { bit_cast<T**>(m_cells.data()), m_cells.size() }; }
+
+    auto begin() { return span().begin(); }
+    auto begin() const { return span().begin(); }
+
+    auto end() { return span().begin(); }
+    auto end() const { return span().begin(); }
+};
+
+}