code: function _empty( x, y, force ) {
              if ( x < 0 || x >= that.width || y < 0 || y >= that.height ) return;
  
              var pos = that.pos(x, y);
              var d = that.grid[pos];
  
              if (d && (d & SLAB_MASK) && (force || !(d & APPLE_MASK))) {
  
                  that.grid[pos] &= ~SLAB_MASK; // clear out slab
  
                  // Clear next neighbor if this is empty tile
                  if (that.grid[pos] == 0) {
                      _empty(x, y - 1) // north
                      _empty(x, y + 1) // south
                      _empty(x - 1, y) // west
                      _empty(x - 1, y - 1) // north west
                      _empty(x - 1, y + 1) // south east
                      _empty(x + 1, y) // east
                      _empty(x + 1, y - 1) // north east
                      _empty(x + 1, y + 1) // south east
                  }
              }
          }
docs: Check where click hit Recursive function to clear empty areas