Code:

import { ArrayToTree } from './common.js'

var numIslands = function(grid) {
    let count = 0

    const dfs = (i, j) => {
        if (i < 0 || i >= grid.length || j < 0 || j >= grid[i].length || grid[i][j] === '0') {
            return
        }

        grid[i][j] = '0'

        dfs(i - 1, j)
        dfs(i + 1, j)
        dfs(i, j - 1)
        dfs(i, j + 1)
    }

    for (let i = 0; i < grid.length; i++) {
        for (let j = 0; j < grid[i].length; j++) {
            if (grid[i][j] === '1') {
                count++

                dfs(i, j)
            }
        }
        
    }


    return count
};

console.log(numIslands([
    ["1","1","0","0","0"],
    ["1","1","0","0","0"],
    ["0","0","1","0","0"],
    ["0","0","0","1","1"]
  ]))