Move appendArray

src/stats/append.js

@@ -0,0 +1,10 @@
+// Append two arrays in a performant way
+export const appendArray = function (bigArray, smallArray) {
+  const smallArrayLength = smallArray.length
+
+  // eslint-disable-next-line fp/no-loops, fp/no-let, fp/no-mutation
+  for (let index = 0; index !== smallArrayLength; index += 1) {
+    // eslint-disable-next-line fp/no-mutating-methods
+    bigArray.push(smallArray[index])
+  }
+}

src/stats/merge.js

@@ -1,8 +1,11 @@
+import { appendArray } from './append.js'
+
 // Merges two sorted arrays.
 // For better performance, the bigger array should be first.
 // The first array is directly mutated. The second is not mutated.
 // This is faster than just doing `Array.concat()` then `Array.sort()` and has
 // a `O(n)` time complexity.
+// For performance, if `bigArray` is empty, we just copy `smallArray` over.
 export const mergeSort = function (bigArray, smallArray) {
   if (bigArray.length === 0) {
     appendArray(bigArray, smallArray)
@@ -17,17 +20,6 @@ export const mergeSort = function (bigArray, smallArray) {
   mergeValues(bigArray, smallArray)
 }
 
-// For performance, if `bigArray` is empty, we just copy `smallArray` over.
-const appendArray = function (bigArray, smallArray) {
-  const smallArrayLength = smallArray.length
-
-  // eslint-disable-next-line fp/no-loops, fp/no-let, fp/no-mutation
-  for (let index = 0; index !== smallArrayLength; index += 1) {
-    // eslint-disable-next-line fp/no-mutating-methods
-    bigArray.push(smallArray[index])
-  }
-}
-
 // Resize `bigArray` so it can receive the new elements from `smallArray`.
 // Resizing an array is slow, so we do this in the most performant way.
 // Any element could be copied. We're only looking to extend the size of