Stop if there are no remaining living cells

src/Board.tsx

@@ -45,6 +45,11 @@ class Board extends React.Component<{}, State> {
     this.timer = setInterval(() => {
       const grid = generateNewGrid(this.state.grid);
       this.setState({ grid, generations: this.state.generations + 1 });
+
+      if (!grid.map((row) => row.includes(true)).includes(true)) {
+        this.stop();
+        alert(`No more living cells, stopping`);
+      }
     }, this.state.speed);
   };