Positions of Large Groups

Problem statement

In a string s of lowercase letters, these letters form consecutive groups of the same character.

For example, a string like s = "abbxxxxzyy" has the groups "a", "bb", "xxxx", "z", and "yy".

A group is identified by an interval [start, end], where start and end denote the start and end indices (inclusive) of the group. In the above example, "xxxx" has the interval [3,6].

A group is considered large if it has 3 or more characters.

Return the intervals of every large group sorted in increasing order by start index.

Example 1:

Input: s = "abbxxxxzzy"Output: [[3,6]]Explanation: "xxxx" is the only large group with start index 3 and end index 6.

Example 2:

Input: s = "abc"Output: []Explanation: We have groups "a", "b", and "c", none of which are large groups.

Example 3:

Input: s = "abcdddeeeeaabbbcd"Output: [[3,5],[6,9],[12,14]]Explanation: The large groups are "ddd", "eeee", and "bbb".

Constraints:

• 1 <= s.length <= 1000
• s contains lowercase English letters only.

My solution

/**
 * @param {string} s
 * @return {number[][]}
 */
var largeGroupPositions = function(s) {
    const idxs = [];
    
    let i = 0;
    let j = 0;
    
    while (j < s.length) {
        if (s.charAt(i) === s.charAt(j)) {
            j++
        } else {
            idxs.push([i, j - 1])
            i = j;
            j++
        }
    }
    
    idxs.push([i, j - 1])
    return idxs.filter(arr => arr[1] - arr[0] + 1 >= 3)
};