```
var GRID_LEN = grid.length;
var edge = 0;
for(var i = 0; i < GRID_LEN; i++) {
for(var j = 0; j < grid[i].length; j++) {
if(grid[i][j] === 1) edge += getedge(i, j);
}
}
return edge;
function getedge(x, y) {
var sum = 4;
if(x - 1 >= 0 && grid[x-1][y] === 1) sum--;
if(y + 1 < grid[x].length && grid[x][y+1] === 1) sum--;
if(x + 1 < GRID_LEN && grid[x+1][y] === 1) sum--;
if(y - 1 >= 0 && grid[x][y-1] === 1) sum--;
return sum;
}
```