Alliterative random username generator. Example: https://jsfiddle.net/morbandit/e0ta9bxy/

alliterative_usernames.js

/**
 * Generates a random username, preferring alliteration where possible
 * @returns {string} A randomly generated username (e.g. "Perfect Pelican")
 */
export const alliterativeUsername = () => {
  // Initial list from https://github.com/sindresorhus/superb/blob/main/superb-words.json
  const adjectives = [
    "ace", "amazing", "astonishing", "astounding", "awe-inspiring", "awesome", "badass", "beautiful", "bedazzling",
    "best", "breathtaking", "brilliant", "charming", "classy", "cool", "dandy", "dazzling", "delightful", "divine",
    "epic", "excellent", "exceptional", "exquisite", "extraordinary", "fabulous", "fantastic", "fantabulous", "fine",
    "finest", "first-class", "first-rate", "flawless", "funkadelic", "geometric", "glorious", "gnarly", "good",
    "grand", "great", "groovy", "groundbreaking", "happy", "heavenly", "hunky-dory", "impeccable", "impressive",
    "incredible", "jaunty", "jovial", "jubilant", "keen", "kickass", "kryptonian", "laudable", "legendary",
    "lovely", "luminous", "magnificent", "majestic", "marvelous", "mathematical", "mind-blowing", "neat", "nice",
    "noble", "optimal", "original", "outstanding", "peachy", "perfect", "phenomenal", "pioneering", "polished",
    "posh", "praiseworthy", "premium", "priceless", "prime", "primo", "quality", "quick", "quirky", "rad",
    "remarkable", "riveting", "scrumtrulescent", "sensational", "shining", "slick", "smashing", "solid",
    "spectacular", "splendid", "splendiferous", "stellar", "striking", "stunning", "stupendous", "stylish",
    "sublime", "super", "super-duper", "super-excellent", "superb", "superior", "supreme", "sweet", "swell",
    "terrific", "tiptop", "top-notch", "transcendent", "tremendous", "unbeatable", "ultimate", "unreal",
    "valiant", "vibrant", "victorious", "well-made", "wicked", "wonderful", "wondrous", "world-class", "xenial",
    "x-factor", "yare", "youthful", "yummy", "zany", "zealous", "zesty"
  ];

  const animals = [
    "Aardvark", "Albatross", "Alligator", "Alpaca", "Ant", "Anteater", "Antelope", "Ape", "Armadillo", "Donkey",
    "Baboon", "Badger", "Barracuda", "Bat", "Bear", "Beaver", "Bee", "Bison", "Boar", "Buffalo", "Butterfly",
    "Camel", "Capybara", "Caribou", "Cassowary", "Cat", "Caterpillar", "Cattle", "Chamois", "Cheetah", "Chicken",
    "Chimpanzee", "Chinchilla", "Chough", "Clam", "Cobra", "Cockroach", "Cod", "Cormorant", "Coyote", "Crab",
    "Crane", "Crocodile", "Crow", "Curlew", "Deer", "Dinosaur", "Dog", "Dogfish", "Dolphin", "Dotterel", "Dove",
    "Dragonfly", "Duck", "Dugong", "Dunlin", "Eagle", "Echidna", "Eel", "Eland", "Elephant", "Elk", "Emu",
    "Falcon", "Ferret", "Finch", "Fish", "Flamingo", "Fly", "Fox", "Frog", "Gaur", "Gazelle", "Gerbil", "Giraffe",
    "Gnat", "Gnu", "Goat", "Goldfinch", "Goldfish", "Goose", "Gorilla", "Goshawk", "Grasshopper", "Grouse",
    "Guanaco", "Gull", "Hamster", "Hare", "Hawk", "Hedgehog", "Heron", "Herring", "Hippopotamus", "Hornet", "Horse",
    "Human", "Hummingbird", "Hyena", "Ibex", "Ibis", "Jackal", "Jaguar", "Jay", "Jellyfish", "Kangaroo",
    "Kingfisher", "Koala", "Kookabura", "Kouprey", "Kudu", "Lapwing", "Lark", "Lemur", "Leopard", "Lion", "Llama",
    "Lobster", "Locust", "Loris", "Louse", "Lyrebird", "Magpie", "Mallard", "Manatee", "Mandrill", "Mantis",
    "Marten", "Meerkat", "Mink", "Mole", "Mongoose", "Monkey", "Moose", "Mosquito", "Mouse", "Mule", "Narwhal",
    "Newt", "Nightingale", "Octopus", "Okapi", "Opossum", "Oryx", "Ostrich", "Otter", "Owl", "Oyster", "Panther",
    "Parrot", "Partridge", "Peafowl", "Pelican", "Penguin", "Pheasant", "Pig", "Pigeon", "Pony", "Porcupine",
    "Porpoise", "Quail", "Quelea", "Quetzal", "Rabbit", "Raccoon", "Rail", "Ram", "Rat", "Raven", "Red deer",
    "Red panda", "Reindeer", "Rhinoceros", "Rook", "Salamander", "Salmon", "Sand Dollar", "Sandpiper", "Sardine",
    "Scorpion", "Seahorse", "Seal", "Shark", "Sheep", "Shrew", "Skunk", "Snail", "Snake", "Sparrow", "Spider",
    "Spoonbill", "Squid", "Squirrel", "Starling", "Stingray", "Stinkbug", "Stork", "Swallow", "Swan", "Tapir",
    "Tarsier", "Termite", "Tiger", "Toad", "Trout", "Turkey", "Turtle", "Viper", "Vulture", "Wallaby", "Walrus",
    "Wasp", "Weasel", "Whale", "Wildcat", "Wolf", "Wolverine", "Wombat", "Woodcock", "Woodpecker", "Worm", "Wren",
    "Yak", "Zebra"
  ];
  
  // 1. Pick a random animal
  const randomAnimal = animals[Math.floor(Math.random() * animals.length)];
  const firstLetter = randomAnimal.charAt(0).toLowerCase();

  // 2. Find all adjectives that start with the same letter
  const matchingAdjectives = adjectives.filter(adj => adj.charAt(0).toLowerCase() === firstLetter);

  // 3. If we found matching adjectives, pick one
  let randomAdjective;
  if (matchingAdjectives.length > 0) {
    randomAdjective = matchingAdjectives[Math.floor(Math.random() * matchingAdjectives.length)];
  }
  // 4. Fallback: If no alliterative match was found, return a completely random pair
  else {
    randomAdjective = adjectives[Math.floor(Math.random() * adjectives.length)];
  }
  
  // 5. Return in title case
  return `${randomAdjective} ${randomAnimal}`.toLowerCase().replace(/\b\w/g, s => s.toUpperCase());
}