floodFill.js

const floodFill = (grid = [], startPoint, newColor) => {
  const [y, x] = startPoint;

  const startColor = grid[y][x];
  const points = [startPoint];
  while (points.length) {
    const [y, x] = points.shift();
 
    grid[y][x] = null;

    if (y - 1 >= 0 && grid[y - 1][x] === startColor) {
      points.push([y - 1, x]);
    }
    if (x + 1 < grid[y].length && grid[y][x + 1] === startColor) {
      points.push([y, x + 1]);
    }
    if (y + 1 < grid.length && grid[y + 1][x] === startColor) {
      points.push([y + 1, x]);
    }
    if (x - 1 >= 0 && grid[y][x - 1] === startColor) {
      points.push([y, x - 1]);
    }
  }
    
  for (let y = 0; y < grid.length; y++) {
    for (let x = 0; x < grid[y].length; x++) {
      if (grid[y][x] === null) {
        grid[y][x] = newColor;
      }
    }
  }

  return grid;
};

function printGrid(grid = []) {
  const height = grid.length;

  let gridStr = "";
  for (let y = 0; y < height; y++) {
    gridStr += `${grid[y].join(" ")}\n`;
  }

  console.log(gridStr);
}

const grids = [
  {
    grid: [
      [0, 0, 3, 3, 3],
      [0, 3, 3, 0, 3],
      [3, 3, 3, 0, 3],
      [0, 3, 0, 0, 3],
      [0, 0, 0, 0, 0]
    ],
    point: [2, 2]
  },
  {
    grid: [
      [0, 1, 0, 2, 0],
      [0, 1, 0, 1, 0],
      [0, 0, 0, 1, 0],
      [0, 0, 0, 1, 0],
      [0, 0, 0, 1, 0]
    ],
    point: [0, 0]
  }
];

const fillColor = 5;

for (let { grid, point } of grids) {
  console.log("original grid:");
  printGrid(grid);

  const newGrid = floodFill(grid, point, fillColor);

  console.log("filled grid:");
  printGrid(newGrid);
}