core: frontend: cosmos: Add Array.last

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

core/frontend/src/cosmos.ts

@@ -3,6 +3,7 @@ export {}
 declare global {
     interface Array<T> {
         first(): T | undefined;
+        last(): T | undefined;
         isEmpty(): boolean;
     }
 
@@ -18,6 +19,11 @@ Array.prototype.first = function<T> (this: T[]): T | undefined {
   return this.isEmpty() ? undefined : this[0]
 }
 
+// eslint-disable-next-line
+Array.prototype.last = function<T> (this: T[]): T | undefined {
+  return this.at(-1)
+}
+
 // eslint-disable-next-line
 Array.prototype.isEmpty = function<T> (this: T[]): boolean {
   return this.length === 0