const sudokuGrid = [
  [5, 3, 0, 0, 7, 0, 0, 0, 0],
  [6, 0, 0, 1, 9, 5, 0, 0, 0],
  [0, 9, 8, 0, 0, 0, 0, 6, 0],
  [8, 0, 0, 0, 6, 0, 0, 0, 3],
  [4, 0, 0, 8, 0, 3, 0, 0, 1],
  [7, 0, 0, 0, 2, 0, 0, 0, 6],
  [0, 6, 0, 0, 0, 0, 2, 8, 0],
  [0, 0, 0, 4, 1, 9, 0, 0, 5],
  [0, 0, 0, 0, 8, 0, 0, 7, 9]
];

function solveSudoku(grid) {
 //iterate over every cell in grid
  for (let row = 0; row < 9; row++) {
    for (let col = 0; col < 9; col++) {
      if (grid[row][col] === 0) {
        for (let num = 1; num <= 9; num++) {
 //check if num can be placed in current cell
          if (isValid(grid, row, col, num)) {
            grid[row][col] = num;

            if (solveSudoku(grid)) {
              return grid;
            }

            grid[row][col] = 0;
          }
        }
        return false;
      }
    }
  }
 //if prgram doesnt break before reaching here, all cells are filled
  return true;
}

console.log(solveSudoku(sudokuGrid));