I am tryng to understand the module pattern and i am having a difficulty understanding why does a declared variable inside prompts an error when i call it in console versus no error when simply modifing it. in the example bellow, if i type "board" on console while i use "let board" an error prompts up. But if i type "board" on console while i use just "board" in js it is OK.

const gameBoard = (function(){
  board = //OK , while "let/const board" prompts an error
  [[0,0,0],
   [0,0,0],
   [0,0,0]
 ];

  for(let i=0; i<board.length; i++){
    let row = document.createElement('div');
    row.className='row';
    for(let j=0; j<board[i].length; j++){
      let cell = document.createElement('div');
      cell.className='cell';
      cell.dataset.number=0;
      row.appendChild(cell);
    }
    document.querySelector('.mainPage').appendChild(row)
  }

  return{
    board
  }

})();