@@ -564,28 +564,17 @@ would be much better to just use ES2015/ES6 classes and simply extend the `Array
 **Bad:**
 ```javascript
 Array..diff = function diff(comparisonArray) {
-const values = [];
-const hash = {};
-
-for (const i of comparisonArray) {
-hash[i] = true;
-}
-
-for (const i of this) {
-if (!hash[i]) {
-values.push(i);
-}
-}
-
-return values;
+const hash = new Set(comparisonArray);
+return this.filter(elem => !hash.has(elem));
 };
 ```
 
 **Good:**
 ```javascript
 class SuperArray extends Array {
 diff(comparisonArray) {
-return this.filter(elem => !comparisonArray.includes(elem));
+const hash = new Set(comparisonArray);
+return this.filter(elem => !hash.has(elem));
 }
 }
 ```