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Hostname Validation With RFC 1123 Labels

Validate DNS hostnames label by label, enforcing length limits, allowed characters, hyphen placement and an optional root dot.

JavascriptForm Validation

Code

snippet
export function isValidHostname(hostname) {
  if (typeof hostname !== "string") throw new TypeError("hostname must be a string");
  const value = hostname.endsWith(".") ? hostname.slice(0, -1) : hostname;
  if (value.length === 0 || value.length > 253) return false;
  return value.split(".").every((label) => {
    if (label.length < 1 || label.length > 63) return false;
    return /^[a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?$/.test(label);
  });
}

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