Add comments to Cartesian Product function.

src/algorithms/sets/cartesian-product/cartesianProduct.js

@@ -1,15 +1,27 @@
+/**
+ * Generates Cartesian Product of two sets.
+ * @param {*[]} setA
+ * @param {*[]} setB
+ * @return {*[]}
+ */
 export default function cartesianProduct(setA, setB) {
+  // Check if input sets are not empty.
+  // Otherwise return null since we can't generate Cartesian Product out of them.
   if (!setA || !setB || !setA.length || !setB.length) {
     return null;
   }
 
+  // Init product set.
   const product = [];
 
+  // Now, let's go through all elements of a first and second set and form all possible pairs.
   for (let indexA = 0; indexA < setA.length; indexA += 1) {
     for (let indexB = 0; indexB < setB.length; indexB += 1) {
+      // Add current product pair to the product set.
       product.push([setA[indexA], setB[indexB]]);
     }
   }
 
+  // Return cartesian product set.
   return product;
 }