Validation

const isEmail = (email) =>
  /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email);

isEmail("user@example.com");     // true
isEmail("user.name+tag@co.uk"); // true
isEmail("not-an-email");        // false
isEmail("missing@domain");      // false

const isURL = (url) => {
  try {
    new URL(url);
    return true;
  } catch {
    return false;
  }
};

isURL("https://example.com");       // true
isURL("http://localhost:3000/api"); // true
isURL("just some text");           // false

const isPhone = (phone) =>
  /^\+?[\d\s\-().]{7,15}$/.test(phone);

isPhone("+1 (555) 123-4567"); // true
isPhone("+91 9876543210");    // true
isPhone("555-1234");          // true
isPhone("abc");               // false

const isStrongPassword = (password) =>
  /^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[\W_]).{8,}$/.test(password);

isStrongPassword("Passw0rd!");   // true
isStrongPassword("password");    // false (no uppercase, number, or special char)
isStrongPassword("PASSWORD1!");  // false (no lowercase)
isStrongPassword("Pass1!");      // false (too short)

const passwordStrength = (password) => {
  let score = 0;
  if (password.length >= 8) score++;
  if (/[a-z]/.test(password)) score++;
  if (/[A-Z]/.test(password)) score++;
  if (/\d/.test(password)) score++;
  if (/[\W_]/.test(password)) score++;
  return score; // 0 = very weak, 4-5 = strong
};

passwordStrength("hello");       // 1
passwordStrength("Hello1");      // 3
passwordStrength("Hello1!");     // 4
passwordStrength("Hello1!xyz");  // 5

const isCreditCard = (number) => {
  const cleaned = number.replace(/\D/g, "");
  if (cleaned.length < 13 || cleaned.length > 19) return false;
  let sum = 0;
  let isEven = false;
  for (let i = cleaned.length - 1; i >= 0; i--) {
    let digit = parseInt(cleaned[i], 10);
    if (isEven) {
      digit *= 2;
      if (digit > 9) digit -= 9;
    }
    sum += digit;
    isEven = !isEven;
  }
  return sum % 10 === 0;
};

isCreditCard("4532015112830366"); // true (Visa test number)
isCreditCard("1234567890123456"); // false
isCreditCard("4532 0151 1283 0366"); // true (spaces ok)

const isDate = (value) => {
  const date = new Date(value);
  return !isNaN(date.getTime());
};

isDate("2024-11-08");          // true
isDate("November 8, 2024");   // true
isDate("not a date");         // false
isDate(new Date());           // true

const isInteger = (value) => Number.isInteger(Number(value));

isInteger(42);      // true
isInteger("42");    // true
isInteger(3.14);    // false
isInteger("3.14");  // false

const isAlpha = (str) => /^[a-zA-Z]+$/.test(str);

isAlpha("Hello");   // true
isAlpha("Hello1");  // false
isAlpha("Hi!");     // false

const isAlphanumeric = (str) => /^[a-zA-Z0-9]+$/.test(str);

isAlphanumeric("Hello123"); // true
isAlphanumeric("Hello!");   // false

const isHexColor = (color) => /^#([0-9A-Fa-f]{3}|[0-9A-Fa-f]{6})$/.test(color);

isHexColor("#fff");    // true
isHexColor("#ffffff"); // true
isHexColor("#AABBCC"); // true
isHexColor("fff");     // false (missing #)
isHexColor("#12345");  // false (wrong length)

const isIPv4 = (ip) =>
  /^(25[0-5]|2[0-4]\d|[01]?\d\d?)(\.(25[0-5]|2[0-4]\d|[01]?\d\d?)){3}$/.test(ip);

isIPv4("192.168.1.1");  // true
isIPv4("255.255.255.0"); // true
isIPv4("999.1.1.1");    // false
isIPv4("192.168.1");    // false

const isUUID = (str) =>
  /^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i.test(str);

isUUID("550e8400-e29b-41d4-a716-446655440000"); // true
isUUID("not-a-uuid");                           // false

const isJSON = (str) => {
  try {
    JSON.parse(str);
    return true;
  } catch {
    return false;
  }
};

isJSON('{"key":"value"}'); // true
isJSON("[1, 2, 3]");       // true
isJSON("not json");        // false