इनपुट वैलिडेशन और एस्केपिंग की मूल बातें

// Escape a few risky characters before displaying in HTML contexts
function escapeText(s) {
  if (typeof s !== "string") return "";
  return s
    .replaceAll("&", "&")
    .replaceAll("<", "&lt;")
    .replaceAll(">", "&gt;")
    .replaceAll("\"", "&quot;")
    .replaceAll("'", "&#39;");
}

console.log("escaped:", escapeText("<b>Hello & bye</b>"));

// Allowlist example: only certain country codes
const ALLOWED = new Set(["TR", "US", "DE", "GB"]);

function parseCountry(code) {
  if (typeof code !== "string") return null;
  const up = code.trim().toUpperCase();
  if (!ALLOWED.has(up)) return null; // reject unknown
  return up; // normalized
}

console.log("country ok:", parseCountry("tr"));
console.log("country bad:", parseCountry("xx"));

// Validate a tiny user object and normalize
function validateUser(input) {
  if (typeof input !== "object" || input === null) return null;

  const nameOk = typeof input.name === "string" && input.name.trim().length >= 1 && input.name.trim().length <= 40;
  const ageOk = parseAge(input.age) !== null;

  if (!nameOk || !ageOk) return null;

  return {
    name: input.name.trim(),
    age: parseAge(input.age)
  };
}

console.log("user ok:", validateUser({ name: " Ayla ", age: "22" }));
console.log("user bad:", validateUser({ name: "", age: "old" }));