Functional JS Columnar transposition cipher

transpose.js

const transposeEncryptMessage = (string, col) => [...Array(col)].map((_, i) => [...Array(Math.ceil(string.length / col))].reduce((acc, _, n) => {
    if (n * col + i < string.length)
        acc += string[n * col + i]
    return acc;
}, [])).join('');

col = 8;
string = "Cenoonommstmme oo snnio. s s c";
len = string.length;
rows = Math.ceil(len / col);
rem = rows * col - len;
[...Array(rows)].map((_, i) => [...Array(col)].reduce((acc, _, n) => {
    let c = n * rows + i + (n*rows >= (len-rem)?-1:0);
	if (c < len && i*n<=col*rows/2+1)
		acc += string[c]
    return acc;
}, [])).join('')