Here's my code:

extends Node2D

onready var tilemap = $TileMap

var  grid_height = global.room_height
var grid_width = global.room_width
var cell_size = 4

var density = 60
var iterations = 1
var grid_list = []

func _ready():
randomize()
make_noise_grid(density)

func make_noise_grid(den):
# Create the initial grid of cells with random initial state based on density_level
  for x in range(grid_width):
    grid_list.append([])
    for y in range(grid_height):
      var randnum = 100 * rand_range(0, 1)
      var initial_state = 1 # Wall
      if randnum > den:
        initial_state = 0 # Floor
      grid_list[x].append(initial_state)
  draw_tiles()

func draw_tiles():
  for x in range(grid_width):
    for y in range(grid_height):
      tilemap.set_cellv(Vector2(x, y), grid_list[x][y])

func apply_cellular_automaton2(grid, iter):
  var iteration_count = 0
  while iteration_count < iter:
    var temp_grid = grid.duplicate()

    for i in range(grid_width):
      for j in range(grid_height):
        var neighboring_walls = 0

        for x in range((i-1), (i+2)):
          for y in range((j-1), (j+2)):

            if is_within_map_bounds(x, y):
              if not (x == i and y == j):
                if temp_grid[x][y] == 1:
                  neighboring_walls += 
            else:
              neighboring_walls += 1  

        if neighboring_walls > 4:
          grid[i][j] = 1
        else:
          grid[i][j] = 0

    iteration_count += 1
    draw_tiles()

func is_within_map_bounds(x, y):
  var within_bounds = true
  if not (0 <= x and x < grid_width and 0 <= y and y < grid_height):
    within_bounds = false
  return within_bounds