https://pastebin.com/yZvZwLAC - код

1.     Array Extension

Extend the build-in Array object with additional functionality. Implement the following functionality:

• - returns the last element of the array
• - returns a new array which includes all original elements, except the first n elements; n is a Number parameter
• - returns a new array containing the first n elements from the original array; n is a Number parameter
• - returns a sum of all array elements
• - returns the average of all array elements

Input / Output

Input for functions that expect it will be passed as valid parameters. Output from functions should be their return value.

Constraints

Structure your code as an IIFE.

https://judge.softuni.bg/Contests/Compete/Index/1677#0

Условието беше с грешка поради използването на arrow функции ! .. До 50 точки я докарах и не знам.. 2и и 3и тест гърмят !

(Unexpected error: Incorrect average value: expected NaN to equal 2);

Благодаря предварително :)