Complete the JavaScript function countSubstrings to count the number of unique substrings in a given string that contain exactly k distinct characters. The function takes two parameters:
string: A string consisting only of lowercase alphabets.k: An integer representing the desired number of distinct characters in a substring.
The function should identify all unique substrings in string that have exactly k distinct characters and return the count of these substrings. Additionally, it should log the distinct substrings to the console in the following format:
Distinct substrings with exactly <k> distinct characters: [substrings array]