CODEWITHSUNDEEP
javascriptregex
Maryam
Maryam

Reputation: 41

Why my regex does not match the 'username' constraints

I am struggling to write a regex on code camp which must fit the following 4 constraints defined for a correct 'username'

1) Usernames can only use alpha-numeric characters.

2) The only numbers in the username have to be at the end. There can be zero or more of them at the end. Username cannot start with the number.

3) Username letters can be lowercase and uppercase.

4) Usernames have to be at least two characters long. A two-character username can only use alphabet letters as characters.

Here is the Regex I came up with, in the following code (first line)

let userCheck = /[a-zA-Z]([a-zA-Z]+\d*|\d\d+)/; // the regex I wrote
let result = userCheck.test(username);

However, it displays the following fault 

Your regex should not match BadUs3rnam3
Your regex should not match c57bT3

I am absolutely confused. I actually know what the correct regex to this problem is, however, I need to know where my own regex is going wrong which is producing the above error. Please help

Upvotes: 1

Views: 1257

Answers (2)

Jyotirmoy
Jyotirmoy

Reputation: 51

Since this question is on free Code Camp and i have also attempted this one with the help of the hit given by them which suggests this as the solution

let username = "JackOfAllTrades";
let userCheck = /^[a-z][a-z]+\d*$|^[a-z]\d\d+$/i;
let result = userCheck.test(username);
console.log(result)

but in my opinion the above regex pattern does not conform to the fourth condition that is given in the question which is

Usernames have to be at least two characters long. A two-character username can only use alphabet letters as characters.

Upvotes: 0

The fourth bird
The fourth bird

Reputation: 163632

Your code passes because you are not using anchors so you get a partial match.

You could update the pattern to ^[a-zA-Z](?:[a-zA-Z]+\d*|\d{2,})$

Another way to write it could be matching either 2 chars a-zA-Z and 0+ digits, or in case there is a single char a-zA-Z, match 2 or more digits to pass the rule A two-character username can only use alphabet letters as characters.

^(?:[a-zA-Z]{2,}\d*|[a-zA-Z]\d{2,})$

Regex demo

let userCheck = /^[a-zA-Z](?:[a-zA-Z]+\d*|\d{2,})$/;
[
  "BadUs3rnam3",
  "c57bT3",
  "aa",
  "a111111",
  "a1",
  "11"
].forEach(username => console.log(username + ": " + userCheck.test(username)));

Upvotes: 1

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