```typescript
export function mergeIntervals(intervals: number[][]): number[][] {
  if (intervals.length === 0) return [];

  intervals.sort(([startA], [startB]) => startA - startB);

  const merged: number[][] = [intervals[0]];

  for (let i = 1; i < intervals.length; i++) {
    const currentInterval = intervals[i];
    const lastMerged = merged[merged.length - 1];

    if (currentInterval[0] <= lastMerged[1]) {
      // Merge overlapping or touching intervals
      lastMerged[1] = Math.max(lastMerged[1], currentInterval[1]);
    } else {
      // Add the non-mergeable interval to the result
      merged.push(currentInterval);
    }
  }

  return merged;
}
```