recursiveSumArrayElement.js

// recursion 1 - using helper function
const RecursiveHelperSumArr = (arr) => {
    let index = arr.length - 1;

    // helper function
    const recur = (curIndex, sum) => { 
      sum += arr[curIndex];
      if (curIndex === 0) return sum;
      return recur(curIndex - 1, sum); // decrement the index and recursion
    }
  
    return recur(index, 0);
}

// recursion 2 - using built-in slice
const RecursiveSliceSumArr = (arr) => {
    return (arr.length === 0) ? 0 : arr[0] + RecursiveSliceSumArr(arr.slice(1));
}


const arr = [1,2,3,4,5]; // ==> 15
console.log(RecursiveHelperSumArr(arr));
console.log(RecursiveSliceSumArr(arr));