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

  const sortedIntervals = intervals.sort((a, b) => a[0] - b[0]);

  let merged: number[][] = [];
  let currentInterval = sortedIntervals[0];

  for (let i = 1; i < sortedIntervals.length; i++) {
    const nextInterval = sortedIntervals[i];
    if (nextInterval[0] <= currentInterval[1]) {
      // Merge the intervals
      currentInterval[1] = Math.max(currentInterval[1], nextInterval[1]);
    } else {
      // Add the current interval to the merged list and move to the next interval
      merged.push([...currentInterval]);
      currentInterval = nextInterval;
    }
  }

  // Add the last remaining interval
  merged.push([...currentInterval]);

  return merged;
}
```