1. Accumulate the total sum with Array

This way is the implement recursion by processing one element at a time with arr[0] + sumArray(arr.slice(1))

function sumArray(arr) {
    if (arr.length === 0) {
        return 0;  // Base case: empty array sums to 0
    }
    
    // Recursive case: head + sum of tail
    return arr[0] + sumArray(arr.slice(1));  
}

console.log(sumArray([1, 2, 3]));  // 6