countNeighbours Cells -

gameOfLife.js countNeighbours

 // Edges should be handle differently as they won't have 8 cells serrounding them
 // Grid Corners will have 3 neighbours only
 // Rows and Columns Edges will have only 5 neighbours
 // All Other cells will have 8 neighbours
 // Iterate between -1 to 2 will allow to go to each neighbour cell from all sides

countNeighbours(grid, currentColumn, currentRow, lastColumn, lastRow) {
     // Getting iterators positions relative to this current column and row
     const { xStart, xEnd, yStart, yEnd } = this.getNeighbourhoodCells(currentColumn, currentRow, lastColumn, lastRow);
     // Build our neighbourhood array
     let neighbourhood = [];
     for (let i = xStart; i < xEnd; i++) {
         for (let j = yStart; j < yEnd; j++) {
             // Skip the current cell
             if (i === 0 && j === 0) {
                 continue;
             }
             
             // Shift the grid column and row based on our iterator
             neighbourhood.push(grid[i + currentColumn][j + currentRow]);
         }
     }
     // Sum all neighbourhood values in the array
     return neighbourhood.reduce((a, b) => a + b, 0);
}