```ts
function mergeIntervals(intervals: number[][]): number[][] {
  if (intervals.some(interval => interval[0] > interval[1])) {
    throw new Error('Invalid interval');
  }

  intervals.sort(([aA], [bB]) => aA - bB);

  const merged: number[][] = [];
  let currentInterval: number[] | undefined;

  for (const interval of intervals) {
    if (!currentInterval || currentInterval[1] < interval[0]) {
      if (currentInterval) {
        merged.push(currentInterval);
      }
      currentInterval = interval;
    } else {
      currentInterval[1] = Math.max(currentInterval[1], interval[1]);
    }
  }

  if (currentInterval) {
    merged.push(currentInterval);
  }

  return merged;
}
```