diff --git a/src/observable/list/SortedMapList.js b/src/observable/list/SortedMapList.js
index 7f525fff..a3479be0 100644
--- a/src/observable/list/SortedMapList.js
+++ b/src/observable/list/SortedMapList.js
@@ -1,5 +1,5 @@
 import BaseObservableList from "./BaseObservableList.js";
-
+import sortedIndex from "../../utils/sortedIndex";
 
 /*
 
@@ -25,35 +25,6 @@ so key -> Map<key,value> -> value -> node -> *parentNode -> rootNode
 with a node containing {value, leftCount, rightCount, leftNode, rightNode, parentNode}
 */
 
-
-/**
- * @license
- * Based off baseSortedIndex function in Lodash <https://lodash.com/>
- * Copyright JS Foundation and other contributors <https://js.foundation/>
- * Released under MIT license <https://lodash.com/license>
- * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
- * Copyright Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
- */
-function sortedIndex(array, value, comparator) {
-    let low = 0;
-    let high = array.length;
-
-    while (low < high) {
-        let mid = (low + high) >>> 1;
-        let cmpResult = comparator(value, array[mid]);
-
-        if (cmpResult > 0) {
-            low = mid + 1;
-        } else if (cmpResult < 0) {
-            high = mid;
-        } else {
-            low = high = mid;
-        }
-    }
-    return high;
-}
-
-
 // does not assume whether or not the values are reference
 // types modified outside of the collection (and affecting sort order) or not
 
diff --git a/src/utils/sortedIndex.js b/src/utils/sortedIndex.js
new file mode 100644
index 00000000..70eaa9b8
--- /dev/null
+++ b/src/utils/sortedIndex.js
@@ -0,0 +1,26 @@
+/**
+ * @license
+ * Based off baseSortedIndex function in Lodash <https://lodash.com/>
+ * Copyright JS Foundation and other contributors <https://js.foundation/>
+ * Released under MIT license <https://lodash.com/license>
+ * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
+ * Copyright Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
+ */
+export default function sortedIndex(array, value, comparator) {
+    let low = 0;
+    let high = array.length;
+
+    while (low < high) {
+        let mid = (low + high) >>> 1;
+        let cmpResult = comparator(value, array[mid]);
+
+        if (cmpResult > 0) {
+            low = mid + 1;
+        } else if (cmpResult < 0) {
+            high = mid;
+        } else {
+            low = high = mid;
+        }
+    }
+    return high;
+}