function getNumberOfNeighbors(cells, currentCell){
    return [
      [-1,-1], [-1, 0], [-1,1],
      [0,-1], [0,1],
      [1,-1], [1,0], [1,1] ].reduce(function(sum,c){
      var cell = [currentCell[0]+c[0], currentCell[1]+c[1]]
      return sum += cells.contains(cell)?1:0
    }, 0)
}
// example:
console.log(
  getNumberOfNeighbors([ [0,0], [0,2], [2,2] ], [0,1])
); // prints 2