Username Regex

const pattern = /^[a-zA-Z0-9_]{3,16}$/;
const text = "john_doe";

// Test if string matches
if (pattern.test(text)) {
  console.log("Valid!");
}

// Extract matches
const matches = text.match(pattern);
console.log(matches);

import re

pattern = r'^[a-zA-Z0-9_]{3,16}$'
text = "john_doe"

# Test if string matches
if re.match(pattern, text):
    print("Valid!")

# Find all matches
matches = re.findall(pattern, text)
print(matches)

<?php
$pattern = '/^[a-zA-Z0-9_]{3,16}$/';
$text = "john_doe";

// Test if string matches
if (preg_match($pattern, $text)) {
    echo "Valid!";
}

// Find all matches
preg_match_all($pattern, $text, $matches);
print_r($matches);
?>

import java.util.regex.*;

String pattern = "^[a-zA-Z0-9_]{3,16}$";
String text = "john_doe";

Pattern p = Pattern.compile(pattern);
Matcher m = p.matcher(text);

if (m.matches()) {
    System.out.println("Valid!");
}