Tell us what’s happening:
Describe your issue in detail here.
I don’t even know what is going on and how this work , found the answer on youtube. Could some one explaint to me the code. I only know the first  which is work for the first string. The rest is none on my brain.
Your code so far
let username = "JackOfAllTrades";
const userCheck = /^[a-z]+([a-z]\d*|\d\d+)$/gi;
let result = userCheck.test(username);
Your browser information:
User Agent is: Mozilla/5.0 (X11; Linux x86_64; rv:99.0) Gecko/20100101 Firefox/99.0
Challenge: Regular Expressions - Restrict Possible Usernames