Add method concat

Author: AndriiKot

app5.js

@@ -0,0 +1,7 @@
+const arr1 = [1,2,3];
+const arr2 = [10,20,30];
+
+const arr3 = arr1.concat(arr2);
+
+console.log(arr3)     // [1,2,3,10,20,30]
+