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diff --git a/Userland/Libraries/LibJS/Heap/Allocator.h b/Userland/Libraries/LibJS/Heap/Allocator.h
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+++ b/Userland/Libraries/LibJS/Heap/Allocator.h
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+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/IntrusiveList.h>
+#include <AK/NonnullOwnPtr.h>
+#include <AK/Vector.h>
+#include <LibJS/Forward.h>
+#include <LibJS/Heap/HeapBlock.h>
+
+namespace JS {
+
+class Allocator {
+public:
+    Allocator(size_t cell_size);
+    ~Allocator();
+
+    size_t cell_size() const { return m_cell_size; }
+
+    Cell* allocate_cell(Heap&);
+
+    template<typename Callback>
+    IterationDecision for_each_block(Callback callback)
+    {
+        for (auto& block : m_full_blocks) {
+            if (callback(block) == IterationDecision::Break)
+                return IterationDecision::Break;
+        }
+        for (auto& block : m_usable_blocks) {
+            if (callback(block) == IterationDecision::Break)
+                return IterationDecision::Break;
+        }
+        return IterationDecision::Continue;
+    }
+
+    void block_did_become_empty(Badge<Heap>, HeapBlock&);
+    void block_did_become_usable(Badge<Heap>, HeapBlock&);
+
+private:
+    const size_t m_cell_size;
+
+    typedef IntrusiveList<HeapBlock, &HeapBlock::m_list_node> BlockList;
+    BlockList m_full_blocks;
+    BlockList m_usable_blocks;
+};
+
+}