Generate Latin Square of any size in Jvascript

A useful code I found online. Posting here for future reference.

// returns a random integer in the range [a, b] (inclusive)
function rnd(a, b) {
    let x = Math.floor(Math.random() * (b - a + 1));
    return a + x;
}

// returns a random latin square
function latinSquare(size) {
    let b, i, j, m, n;
    b = [];
    // legally populate board by shifting each row by one
    for (i = 0; i < size; i++) {
        b[i] = [];
        for (j = 0; j < size; j++) {
            b[i][j] = ((i + j) % size) + 1;
        }
    }
    // shuffle rows
    for (m = size - 1; m > 0; m--) {
        n = rnd(0, m); // 0 <= n <= m
        swapRows(b, m, n);
    }
    // shuffle cols
    for (m = size - 1; m > 0; m--) {
        n = rnd(0, m); // 0 <= n <= m
        swapCols(b, m, n);
    }
    return b;
}

// swaps two rows in a latin square
function swapRows(a, m, n) {
    let swap = a[m];
    a[m] = a[n];
    a[n] = swap;
}

// swaps two columns in a latin square
function swapCols(a, m, n) {
    let j, swap;
    for (j = 0; j < a[m].length; j++) {
        swap = a[j][m];
        a[j][m] = a[j][n];
        a[j][n] = swap;
    }
}

let latin = latinSquare(8);
console.log(latin);