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diff --git a/js/src/ds/PriorityQueue.h b/js/src/ds/PriorityQueue.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * 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 ds_PriorityQueue_h
+#define ds_PriorityQueue_h
+
+#include "js/Vector.h"
+
+namespace js {
+
+/*
+ * Class which represents a heap based priority queue using a vector.
+ * Inserting elements and removing the highest priority one are both O(log n).
+ *
+ * Template parameters are the same as for Vector, with the addition that P
+ * must have a static priority(const T&) method which returns higher numbers
+ * for higher priority elements.
+ */
+template <class T, class P, size_t MinInlineCapacity = 0,
+          class AllocPolicy = TempAllocPolicy>
+class PriorityQueue {
+  Vector<T, MinInlineCapacity, AllocPolicy> heap;
+
+  PriorityQueue(const PriorityQueue&) = delete;
+  PriorityQueue& operator=(const PriorityQueue&) = delete;
+
+ public:
+  explicit PriorityQueue(AllocPolicy ap = AllocPolicy())
+      : heap(std::move(ap)) {}
+
+  [[nodiscard]] bool reserve(size_t capacity) { return heap.reserve(capacity); }
+
+  size_t length() const { return heap.length(); }
+
+  bool empty() const { return heap.empty(); }
+
+  T removeHighest() {
+    T highest = heap[0];
+    T last = heap.popCopy();
+    if (!heap.empty()) {
+      heap[0] = last;
+      siftDown(0);
+    }
+    return highest;
+  }
+
+  [[nodiscard]] bool insert(const T& v) {
+    if (!heap.append(v)) {
+      return false;
+    }
+    siftUp(heap.length() - 1);
+    return true;
+  }
+
+  void infallibleInsert(const T& v) {
+    heap.infallibleAppend(v);
+    siftUp(heap.length() - 1);
+  }
+
+ private:
+  /*
+   * Elements of the vector encode a binary tree:
+   *
+   *      0
+   *    1   2
+   *   3 4 5 6
+   *
+   * The children of element N are (2N + 1) and (2N + 2).
+   * The parent of element N is (N - 1) / 2.
+   *
+   * Each element has higher priority than its children.
+   */
+
+  void siftDown(size_t n) {
+    while (true) {
+      size_t left = n * 2 + 1;
+      size_t right = n * 2 + 2;
+
+      if (left < heap.length()) {
+        if (right < heap.length()) {
+          if (P::priority(heap[n]) < P::priority(heap[right]) &&
+              P::priority(heap[left]) < P::priority(heap[right])) {
+            swap(n, right);
+            n = right;
+            continue;
+          }
+        }
+
+        if (P::priority(heap[n]) < P::priority(heap[left])) {
+          swap(n, left);
+          n = left;
+          continue;
+        }
+      }
+
+      break;
+    }
+  }
+
+  void siftUp(size_t n) {
+    while (n > 0) {
+      size_t parent = (n - 1) / 2;
+
+      if (P::priority(heap[parent]) > P::priority(heap[n])) {
+        break;
+      }
+
+      swap(n, parent);
+      n = parent;
+    }
+  }
+
+  void swap(size_t a, size_t b) {
+    T tmp = heap[a];
+    heap[a] = heap[b];
+    heap[b] = tmp;
+  }
+};
+
+} /* namespace js */
+
+#endif /* ds_PriorityQueue_h */