Find all substrings containing just unique values of a given length from a given string

uniqueValuesSubstrings.js

// Example: "kjzskjkjk" 3 => [ "kjz", "jzs", "zsk", "skj" ]

function justUniqueVals(arr) {
    return arr.filter((item, index, self) => self.indexOf(item) == index);
    // not performant for long arrays!!! use  occurences hashmap instead
}

function hasUniqueVals(arr) {
    const filtered = justUniqueVals(arr);
    return filtered.length == arr.length;
}

function substrings(string, num) {
    const result = [];
    if (string.length < num ||
        string.length == 0 ||
        (string.length == num && !hasUniqueVals)
    ) {
        return result;
    }

    const input = string.split("");

    input.forEach((letter, index) => {

        const substring = input.slice(index, index + num);

        if (substring.length == num && hasUniqueVals(substring)) {
            result.push(substring);
        }
    });

    return justUniqueVals(result).sort();
}