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

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

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

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

  // Add the last interval if there's anything left
  if (currentInterval) {
    merged.push([...currentInterval]);
  }

  return merged;
}
```