Add initial code listings

Listing_6.7.js

@@ -0,0 +1,20 @@
+.
+.
+.
+let numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+
+// sum: Imperative solution
+function imperativeSum(elements) {
+  let total = 0;
+  elements.forEach(function(n) {
+    total += n;
+  });
+  return total;
+}
+console.log(imperativeSum(numbers));
+
+// sum: Functional solution
+function functionalSum(elements) {
+  return elements.reduce((total, n) => { return total += n; });
+}
+console.log(functionalSum(numbers));