Add stableSort function

test/stableSort/stableSort.js

@@ -0,0 +1,8 @@
+var stableSort = (arr, compare) =>
+arr
+.map((item, index) => ({ item, index }))
+.sort((a, b) =>
+((result = compare(a.item, b.item)) => (result !== 0 ? result : a.index - b.index))()
+)
+.map(({ item }) => item);
+module.exports = stableSort;