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

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

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

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

    merged.push([...currentInterval]);

    return merged;
}
```