LeetCode 56. Merge Intervals

Given a collection of intervals, merge all overlapping intervals.

Example 1:
Input: intervals = [[1,3],[2,6],[8,10],[15,18]]
Output: [[1,6],[8,10],[15,18]]
Explanation: Since intervals [1,3] and [2,6] overlaps, merge them into [1,6].
Example 2:
Input: intervals = [[1,4],[4,5]]
Output: [[1,5]]
Explanation: Intervals [1,4] and [4,5] are considered overlapping.
NOTE: input types have been changed on April 15, 2019. Please reset to default code definition to get new method signature.

Constraints:
intervals[i][0] <= intervals[i][1]

var merge = function(intervals) {
    if(intervals.length <= 1) return intervals;
    // sort the array so earlier start times are at the beginning
    intervals = intervals.sort((a,b) => a[0] - b[0])
    let output = [intervals[0]];
    let current = output[0];
    // If the current interval's end time is greater than or equal 
    // to the next interval's start time, then we know there is an
    // overlap and we merge them.
    // If there is no overlap, then we add the next interval to the 
    // list of intervals in our output array and repeat the process
    // until we go through the entire list of intervals.
    for(let i = 1; i< intervals.length;i++) {
        const next = intervals[i]
        if(current[1] >= next[0]) {
            current[1] = Math.max(current[1], next[1]);
        } else {
            current = next;
            output.push(current);
        }
    }
    return output;
};