@redocly/theme/src/core/utils/is-url.ts

Shared UI components lib

/**
 * RegExps.
 * A URL must match #1 and then at least one of #2/#3.
 * Use two levels of REs to avoid REDOS.
 */

const protocolAndDomainRE = /^(?:\w+:)?\/\/(\S+)$/;

const localhostDomainRE = /^localhost[:?\d]*(?:[^:?\d]\S*)?$/;
const nonLocalhostDomainRE = /^[^\s.]+\.\S{2,}$/;

/**
 * Loosely validate a URL `string`.
 *
 * @param {String} input
 * @return {Boolean}
 */

export function isUrl(input: unknown): boolean {
  if (typeof input !== 'string') {
    return false;
  }

  const match = input.match(protocolAndDomainRE);
  if (!match) {
    return false;
  }

  const everythingAfterProtocol = match[1];
  if (!everythingAfterProtocol) {
    return false;
  }

  if (
    localhostDomainRE.test(everythingAfterProtocol) ||
    nonLocalhostDomainRE.test(everythingAfterProtocol)
  ) {
    return true;
  }

  return false;
}