diff --git a/js/src/jsutil.h b/js/src/jsutil.h
index 02fe9fe10c8d..b46b118d880d 100644
--- a/js/src/jsutil.h
+++ b/js/src/jsutil.h
@@ -22,6 +22,7 @@
 #include "js/Initialization.h"
 #include "js/Utility.h"
 #include "js/Value.h"
+#include "util/BitArray.h"
 #include "util/Poison.h"
 
 /* Crash diagnostics by default in debug and on nightly channel. */
@@ -88,56 +89,6 @@ static constexpr T AlignBytes(T bytes, U alignment) {
 
 /*****************************************************************************/
 
-/* A bit array is an array of bits represented by an array of words (size_t). */
-
-static const size_t BitArrayElementBits = sizeof(size_t) * CHAR_BIT;
-
-static inline unsigned NumWordsForBitArrayOfLength(size_t length) {
-  return (length + (BitArrayElementBits - 1)) / BitArrayElementBits;
-}
-
-static inline unsigned BitArrayIndexToWordIndex(size_t length,
-                                                size_t bitIndex) {
-  unsigned wordIndex = bitIndex / BitArrayElementBits;
-  MOZ_ASSERT(wordIndex < length);
-  return wordIndex;
-}
-
-static inline size_t BitArrayIndexToWordMask(size_t i) {
-  return size_t(1) << (i % BitArrayElementBits);
-}
-
-static inline bool IsBitArrayElementSet(const size_t* array, size_t length,
-                                        size_t i) {
-  return array[BitArrayIndexToWordIndex(length, i)] &
-         BitArrayIndexToWordMask(i);
-}
-
-static inline bool IsAnyBitArrayElementSet(const size_t* array, size_t length) {
-  unsigned numWords = NumWordsForBitArrayOfLength(length);
-  for (unsigned i = 0; i < numWords; ++i) {
-    if (array[i]) {
-      return true;
-    }
-  }
-  return false;
-}
-
-static inline void SetBitArrayElement(size_t* array, size_t length, size_t i) {
-  array[BitArrayIndexToWordIndex(length, i)] |= BitArrayIndexToWordMask(i);
-}
-
-static inline void ClearBitArrayElement(size_t* array, size_t length,
-                                        size_t i) {
-  array[BitArrayIndexToWordIndex(length, i)] &= ~BitArrayIndexToWordMask(i);
-}
-
-static inline void ClearAllBitArrayElements(size_t* array, size_t length) {
-  for (unsigned i = 0; i < length; ++i) {
-    array[i] = 0;
-  }
-}
-
 // Placement-new elements of an array. This should optimize away for types with
 // trivial default initiation.
 template <typename T>
diff --git a/js/src/util/BitArray.h b/js/src/util/BitArray.h
new file mode 100644
index 000000000000..ca83d8d0df49
--- /dev/null
+++ b/js/src/util/BitArray.h
@@ -0,0 +1,71 @@
+/* -*- 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/. */
+
+/*
+ * A bit array is an array of bits represented by an array of words (size_t).
+ */
+
+#ifndef util_BitArray_h
+#define util_BitArray_h
+
+#include "mozilla/Assertions.h"
+
+#include <limits.h>
+#include <stddef.h>
+
+namespace js {
+
+static const size_t BitArrayElementBits = sizeof(size_t) * CHAR_BIT;
+
+static inline unsigned NumWordsForBitArrayOfLength(size_t length) {
+  return (length + (BitArrayElementBits - 1)) / BitArrayElementBits;
+}
+
+static inline unsigned BitArrayIndexToWordIndex(size_t length,
+                                                size_t bitIndex) {
+  unsigned wordIndex = bitIndex / BitArrayElementBits;
+  MOZ_ASSERT(wordIndex < length);
+  return wordIndex;
+}
+
+static inline size_t BitArrayIndexToWordMask(size_t i) {
+  return size_t(1) << (i % BitArrayElementBits);
+}
+
+static inline bool IsBitArrayElementSet(const size_t* array, size_t length,
+                                        size_t i) {
+  return array[BitArrayIndexToWordIndex(length, i)] &
+         BitArrayIndexToWordMask(i);
+}
+
+static inline bool IsAnyBitArrayElementSet(const size_t* array, size_t length) {
+  unsigned numWords = NumWordsForBitArrayOfLength(length);
+  for (unsigned i = 0; i < numWords; ++i) {
+    if (array[i]) {
+      return true;
+    }
+  }
+  return false;
+}
+
+static inline void SetBitArrayElement(size_t* array, size_t length, size_t i) {
+  array[BitArrayIndexToWordIndex(length, i)] |= BitArrayIndexToWordMask(i);
+}
+
+static inline void ClearBitArrayElement(size_t* array, size_t length,
+                                        size_t i) {
+  array[BitArrayIndexToWordIndex(length, i)] &= ~BitArrayIndexToWordMask(i);
+}
+
+static inline void ClearAllBitArrayElements(size_t* array, size_t length) {
+  for (unsigned i = 0; i < length; ++i) {
+    array[i] = 0;
+  }
+}
+
+} /* namespace js */
+
+#endif /* util_BitArray_h */