Sub Sum JS Advanced

function subSum(arr, startIndex, endIndex) {
    if (!Array.isArray(arr)) {
        return NaN;
    }

    if (arr.length === 0) {
        return 0;
    }

    startIndex = Math.max(startIndex, 0);

    endIndex = Math.min(endIndex, arr.length - 1);

    let sum = 0;

    for (let i = startIndex; i <= endIndex; i++) {
        if (typeof arr[i] !== "number") {
            return NaN;
        }
        sum += arr[i];
    }

    return sum;
}