Matrix Diagonals Sum Difference

function isRectangular(rows) {
    if (rows.length > 0) {
        const establishedWidth = rows[0].length;
        return rows.every(row => row.length === establishedWidth);
    }

    throw Error("Can't determine the shape of an empty structure. There needs to be at least one row.");
}

class Matrix {
    constructor(rows) {
        if (!isRectangular(rows)) {
            throw Error("A matrix has to have the same number of columns in each row.");
        }

        this.width = rows[0].length;
        this.height = rows.length;
        this.rows = rows;
    }

    getValue({ x, y }) { return this.rows[y] && this.rows[y][x]; }

    isValidPosition({ x, y }) {
        return x >= 0 && x < this.width &&
            y >= 0 && y < this.height;
    }

    reduce({
        reduceCallback,
        initialValue: accumulator = 0,
        startingPosition: position,
        traversalMethod: getNextPosition
    }) {
        while (this.isValidPosition(position)) {
            accumulator = reduceCallback(accumulator, this.getValue(position));
            position = getNextPosition(position);
        }

        return accumulator;
    }
}

const toBottomRight = ({ x, y }) => ({ x: x + 1, y: y + 1 });
const toBottomLeft = ({ x, y }) => ({ x: x - 1, y: y + 1 });

const sum = (a, b) => a + b;

function diagonalDifference(arr) {
    const matrix = new Matrix(arr);

    const ltr = matrix.reduce({
        reduceCallback: sum,
        startingPosition: { x: 0, y: 0 },
        traversalMethod: toBottomRight
    });

    const rtl = matrix.reduce({
        reduceCallback: sum,
        startingPosition: { x: matrix.width - 1, y: 0 },
        traversalMethod: toBottomLeft
    });

    return Math.abs(ltr - rtl);
}