findMaxIsland

var findLeft = function(grid, row, col) {
  if(col > 0) {
    return grid[row][col - 1];
  } else {
    return undefined;
  }
};

var findRight = function(grid, row, col) {
  if(col < grid[row].length-1) {
    return grid[row][col + 1];
  } else {
    return undefined;
  }
};

var findAbove = function(grid, row, col) {
  if(row > 0) {
    return grid[row - 1][col];
  } else {
    return undefined;
  }
};

var findBelow = function(grid, row, col) {
  if(row < grid.length-1) {
    return grid[row + 1][col];
  } else {
    return undefined;
  }
};

var findBelowRight = function(grid, row, col) {
  if(row < grid.length-1 && col < grid[row].length-1) {
    return grid[row + 1][col + 1];
  } else {
    return undefined;
  }
};

var findBelowLeft = function(grid, row, col) {
  if(row < grid.length-1 && col > 0) {
    return grid[row + 1][col - 1];
  } else {
    return undefined;
  }
};

var findAboveRight = function(grid, row, col) {
  if(row > 0 && col < grid[row].length-1) {
    return grid[row - 1][col + 1];
  } else {
    return undefined;
  }
};

var findAboveLeft = function(grid, row, col) {
  if(row > 0 && col > 0) {
    return grid[row - 1][col - 1];
  } else {
    return undefined;
  }
};

var findIsland = function(grid, row, col, increment) {
  increment();
  grid[row][col] = 0;
  var left = findLeft(grid, row, col);
  if(left) {
    findIsland(grid, row, col - 1, increment);
  }
  var right = findRight(grid, row, col);
  if(right) {
    findIsland(grid, row, col + 1, increment);
  }
  var above = findAbove(grid, row, col);
  if(above) {
    findIsland(grid, row - 1, col, increment);
  }
  var below = findBelow(grid, row, col);
  if(below) {
    findIsland(grid, row + 1, col, increment);
  }
  var belowLeft = findBelowLeft(grid, row, col);
  if(belowLeft) {
    findIsland(grid, row + 1, col - 1, increment);
  }
  var belowRight = findBelowRight(grid, row, col);
  if(belowRight) {
    findIsland(grid, row + 1, col + 1, increment);
  }
  var aboveLeft = findAboveLeft(grid, row, col);
  if(aboveLeft) {
    findIsland(grid, row - 1, col - 1, increment);
  }
  var aboveRight = findRight(grid, row, col);
  if(aboveRight) {
    findIsland(grid, row - 1, col + 1, increment);
  }
  
  
  return grid;
};

var findMaxIsland = function(grid) {
  var islands = [];
  var count = 0;
  var increment = function() { count++ };
  
  for(var i = 0; i < grid.length; i++) {
    for(var j = 0; j < grid[i].length; j++) {
      if(grid[i][j] === 1) {
        findIsland(grid, i, j, increment);
        islands.push(count);
        count = 0;
      }
    }
  }
  return islands.reduce(function(acc, island) {
    if(island > acc) {
      acc = island;
    }
    return acc;
  }, 0);
};

var gridExample = [[0, 1, 0, 0],
                   [1, 1, 0, 0],
                   [1, 1, 0, 0],
                   [0, 0, 0, 0]];

findMaxIsland(gridExample); // => 5