Fischer Random Chess setup generator

Chess960.js

import _ from "lodash";

// [0, 1, 2, 3, 4, 5, 6, 7]
//  b, w, b, w, b, w, b, w

// gets all indices of `chr` in `str`
const getIndices = (chr) => (str) =>
  str
    .split("")
    .map((n, i) => [n, i])
    .filter(([n, _]) => n === chr)
    .map(([_, i]) => i);

// replaces item at index in string
const replace = (index, item) => (string) =>
  string.substring(0, index) + item + string.substring(index + 1);

function blackBishop(board) {
  const spot = _.sample([0, 2, 4, 6]);
  return replace(spot, "b")(board);
}

function whiteBishop(board) {
  const spot = _.sample([1, 3, 5, 7]);
  return replace(spot, "b")(board);
}

function knight(board) {
  const spot = _.flow([getIndices(" "), _.sample])(board);
  return replace(spot, "n")(board);
}

function queen(board) {
  const spot = _.flow([getIndices(" "), _.sample])(board);
  return replace(spot, "q")(board);
}

function rooksAndKing(board) {
  const [r1, k, r2] = getIndices(" ")(board);
  return _.flow([replace(r1, "r"), replace(k, "k"), replace(r2, "r")])(board);
}

// start with 8 blank spaces
const board = _.repeat(" ", 8);

const result = _.flow([
  blackBishop,
  whiteBishop,
  knight,
  knight,
  queen,
  rooksAndKing,
  _.toUpper,
])(board);

console.log(result);