Function resolveBaseUrl

packages/vite/src/node/config.ts:2228–2266

(
  base: UserConfig['base'] = configDefaults.base,
  isBuild: boolean,
  logger: Logger,
)

 * electron or expects to deploy
 */
export function resolveBaseUrl(
  base: UserConfig['base'] = configDefaults.base,
  isBuild: boolean,
  logger: Logger,
): string {
  if (base[0] === '.') {
    logger.warn(
      colors.yellow(
        colors.bold(
          `(!) invalid "base" option: "${base}". The value can only be an absolute ` +
            `URL, "./", or an empty string.`,
        ),
      ),
    )
    return '/'
  }

  // external URL flag
  const isExternal = isExternalUrl(base)
  // no leading slash warn
  if (!isExternal && base[0] !== '/') {
    logger.warn(
      colors.yellow(
        colors.bold(`(!) "base" option should start with a slash.`),
      ),
    )
  }

  // parse base when command is serve or base is not External URL
  if (!isBuild || !isExternal) {
    base = new URL(base, 'http://vite.dev').pathname
    // ensure leading slash
    if (base[0] !== '/') {
      base = '/' + base
    }
  }

  return base
}

function decodeBase(base: string): string {
  try {