Calculate the hourglass sum for every hourglass in array

hourglass-sum.js

// i - row
// j - column

function main() {
    var arr = [];
    var sum = 0;
    var maxSum = -63;
    for(arr_i = 0; arr_i < 6; arr_i++){
       arr[arr_i] = readLine().split(' ');
       arr[arr_i] = arr[arr_i].map(Number);
    }
    for (arr_j = 0; arr_j <= 3; arr_j++) {
        for (arr_i = 0; arr_i <= 3; arr_i++) {
            sum = arr[arr_i][arr_j] + arr[arr_i][arr_j+1] + arr[arr_i][arr_j+2] + arr[arr_i+1][arr_j+1] + arr[arr_i+2]                   [arr_j] + arr[arr_i+2][arr_j+1] + arr[arr_i+2][arr_j+2];
            maxSum = Math.max(maxSum, sum);
        }
    }
    console.log(maxSum);
}