https://eloquentjavascript.net/02_program_structure.html

grid.js

// https://eloquentjavascript.net/02_program_structure.html
// keyword: chessboard
// quiz at the end

const generate = (size = 0) => {
  if (size === 0) {
    return '';
  }

  if (size === 1) {
    return '#';
  }

  let grid = '';
  for (let i = 1; i <= size; i++) {
    for (let j = 1; j <= size + 1; j++) {
      if (j === size + 1) {
        grid += '\n';
        continue;
      }
      
      if (i % 2 !== 0) {
        if (j % 2 !== 0) {
          grid += ' ';
        } else {
          grid += '#';
        }
      } else {
        if (j % 2 !== 0) {
          grid += '#';
        } else {
          grid += ' ';
        }
      }
    } 
  }

  return grid;
}

const grid = generate(10);

console.log(grid);

// simplifying algorithm
const generate = (size = 0) => {
  let grid = '';
  for (let i = 1; i <= size; i++) {
    for (let j = 1; j <= size + 1; j++) {
      if (j === size + 1) {
        grid += '\n';
        continue;
      }
      
      if ((i+j) % 2 !==0) {
        grid += '#';
      } else {
        grid += ' ';
      }
    } 
  }

  return grid;
}

const grid = generate(10);

console.log(grid);