/**
 * Authenticate a list of usernames
 *
 * Given an array of strings representing a list of usernames, return true only if all usernames comply with your
 * company's guidelines. Return false otherwise.
 *
 * it is between 6-10 characters long;
 * contains at least 1 lowercase letter;
 * contains at least 1 number;
 * contains only numbers and lowercase letters.
 */

function authList(arr) {
    return arr.every(v => /^(?=.*[a-z])(?=.*\d)[a-z\d]{6,10}$/.test(v)); //every, positive, negati look ahead, negation
}