Updated solution

SunJieMing · SunJieMing · commit c50caec5f0f2 · 2017-10-02T07:50:50.000-07:00
diff --git a/src/arrays.js b/src/arrays.js
@@ -22,10 +22,11 @@ const map = (elements, cb) => {
   return mappedArr;
 };
 
-const reduce = (elements, cb, memo = elements.shift()) => {
+const reduce = (elements, cb, startingValue = elements.shift()) => {
   // Combine all elements into a single value going from left to right.
   // Elements will be passed one by one into `cb`.
   // `memo` is the starting value.  If `memo` is undefined then make `elements[0]` the initial value.
+  let memo = startingValue;
   each(elements, (item) => {
     memo = cb(memo, item);
   });
