Calculate the sum of numbers from 1 to n using recursion

(function(){
    // Calculate the sum of numbers from 1 to n using recursion.

    const getSum = (arr) => {
       if (arr.length < 1) {
          return 0;
       }

       return arr.pop() + getSum(arr);
    };
 
    const a = [1, 2, 3, 5];
    console.log(getSum(a))
})();