Grid.js

const GRID_SIZE = 3
const CELL_SIZE = 20
const CELL_GAP = 0

export default class Grid {
  #cells

  constructor(gridElement) {
    gridElement.style.setProperty("--grid-size", GRID_SIZE)
    gridElement.style.setProperty("--cell-size", `${CELL_SIZE}vmin`)
    gridElement.style.setProperty("--cell-gap", `${CELL_GAP}vmin`)
    gridElement.style.setProperty("--cell-size-mark", `${CELL_SIZE * 0.8}vmin`)
    gridElement.style.setProperty("--cell-size-o-inner", `${CELL_SIZE * 0.8 * 0.7}vmin`)
    this.#cells = createCellElements(gridElement).map((cellElement, index) => {
      return new Cell(
        cellElement,
        index % GRID_SIZE,
        Math.floor(index / GRID_SIZE)
      )
    })
  }

  get cells() {
    return this.#cells
  }

  get cellsByRow() {
    return this.#cells.reduce((cellGrid, cell) => {
      cellGrid[cell.y] = cellGrid[cell.y] || []
      cellGrid[cell.y][cell.x] = cell
      return cellGrid
    }, [])
  }

  get cellsByColumn() {
    return this.#cells.reduce((cellGrid, cell) => {
      cellGrid[cell.x] = cellGrid[cell.x] || []
      cellGrid[cell.x][cell.y] = cell
      return cellGrid
    }, [])
  }

  get #emptyCells() {
    return this.#cells.filter(cell => cell.tile == null)
  }

  randomEmptyCell() {
    const randomIndex = Math.floor(Math.random() * this.#emptyCells.length)
    return this.#emptyCells[randomIndex]
  }

  getCellByElement(cellElement) {
    return this.#cells.find((cell) => {
      if(cell.cellElement == cellElement)
        return true;
    })
  }

}

class Cell {
  #cellElement
  #x
  #y

  constructor(cellElement, x, y) {
    this.#cellElement = cellElement
    this.#x = x
    this.#y = y
  }

  get x() {
    return this.#x
  }

  get y() {
    return this.#y
  }

  get cellElement() {
    return this.#cellElement
  }
}

function createCellElements(gridElement) {
  const cells = []
  for (let i = 0; i < GRID_SIZE * GRID_SIZE; i++) {
    const cell = document.createElement("div")
    cell.classList.add("cell")
    cells.push(cell)
    gridElement.append(cell)
  }
  return cells
}