SOO HAPPY I DID THIS ONE

nqueensbacktracking.js

const printBoard = (board) => {
    const length = board.length;
    for (let row = 0; row < length; row++) {
        let str = "";
        for (let col = 0; col < length; col++) {
            const current = board[row][col];
            current ? str += "Q" : str += "X";
        }
        console.log(str);
    }
    console.log("");
}
const nQueens = (n) => {
  const board = new Array(n).fill().map(() => new Array(n).fill(false));
  nQueensSolver(board);
  printBoard(board);
};
// place in currentRow
// iterate through row and find a spot to place
const nQueensSolver = (board, currentRow = 0) => {
  if (currentRow === board.length) return true;
  for (let currentCol = 0; currentCol < board.length; currentCol++) {
      board[currentRow][currentCol] = true;
      if (isValidBoard(board)) {
        if(nQueensSolver(board, currentRow + 1)) {
            return true;
        }
        board[currentRow][currentCol] = false;
      } else {
          board[currentRow][currentCol] = false;
      }
  }
  return false;
};
const isValidBoard = (boardToValidate) => {
  const length = boardToValidate.length;
  const checkCol = (col) => {
    let numQueens = 0;
    for (let row = 0; row < length; row++) {
      if (boardToValidate[row][col]) numQueens++;
    }
    return numQueens < 2;
  };
  const upperLeft = (row, col) => {
    // move up and left until we hit wall
    // returns num of queens
    let currentRow = row;
    let currentCol = col;
    let numQueens = 0;
    while (currentRow > -1 && currentCol > -1) {
      if (boardToValidate[currentRow][currentCol]) numQueens++;
      currentCol--;
      currentRow--;
    }
    return numQueens;
  };
  const upperRight = (row, col) => {
    // move up and right until we hit wall
    let currentRow = row;
    let currentCol = col;
    let numQueens = 0;
    while (currentRow > -1 && currentCol < length) {
      if (boardToValidate[currentRow][currentCol]) numQueens++;
      currentCol++;
      currentRow--;
    }
    return numQueens;
  };
  const lowerLeft = (row, col) => {
    // move down and left until we hit wall
    let currentRow = row;
    let currentCol = col;
    let numQueens = 0;
    while (currentRow < length && currentCol > -1) {
      if (boardToValidate[currentRow][currentCol]) numQueens++;
      currentCol--;
      currentRow++;
    }
    return numQueens;
  };
  const lowerRight = (row, col) => {
    // move down and right until we hit wall
    let currentRow = row;
    let currentCol = col;
    let numQueens = 0;
    while (currentRow < length && currentCol < length) {
      if (boardToValidate[currentRow][currentCol]) numQueens++;
      currentCol++;
      currentRow++;
    }
    return numQueens;
  };
  // # queen 0 no queen
  // # 0 0 0
  // 0 0 # 0
  // 0 0 0 0
  // 0 0 0 0
  const checkDiagonal = (row, col) => {
    return (
      upperLeft(row - 1, col - 1) +
        upperRight(row - 1, col + 1) +
        lowerLeft(row + 1, col - 1) +
        lowerRight(row + 1, col + 1) +
        1 <
      2
    );
  };
  for (let row = 0; row < length; row++) {
    for (let col = 0; col < length; col++) {
      const isQueen = boardToValidate[row][col];
      if (isQueen) {
        if (!checkCol(col)) return false;
        if (!checkDiagonal(row, col)) return false;
      }
    }
  }
  return true;
};
// XQXX
// XXXQ
// QXXX
// XXQX
nQueens(4);
// QXXXXXXX
// XXXXQXXX
// XXXXXXXQ
// XXXXXQXX
// XXQXXXXX
// XXXXXXQX
// XQXXXXXX
// XXXQXXXX
nQueens(8);