Routing and Normalization | blade47/next.js Wiki | doc0

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Routing and Normalization | blade47/next.js Wiki | doc0

const cache = new WeakMap<readonly string[], readonly string[]>()
 
export function normalizeLocalePath(
  pathname: string,
  locales?: readonly string[]
): PathLocale {
  if (!locales) return { pathname }
 
  let lowercasedLocales = cache.get(locales)
  if (!lowercasedLocales) {
    lowercasedLocales = locales.map((locale) => locale.toLowerCase())
    cache.set(locales, lowercasedLocales)
  }
 
  const segments = pathname.split('/', 2)
  if (!segments[1]) return { pathname }
 
  const segment = segments[1].toLowerCase()
  const index = lowercasedLocales.indexOf(segment)
  if (index < 0) return { pathname }
 
  const detectedLocale = locales[index]
  pathname = pathname.slice(detectedLocale.length + 1) || '/'
 
  return { pathname, detectedLocale }
}

export function normalizeDataPath(pathname: string) {
  if (!pathHasPrefix(pathname || '/', '/_next/data')) {
    return pathname
  }
  pathname = pathname
    .replace(/\/_next\/data\/[^/]{1,}/, '')
    .replace(/\.json$/, '')
 
  if (pathname === '/index') {
    return '/'
  }
  return pathname
}

export function normalizeAppPath(route: string) {
  return ensureLeadingSlash(
    route.split('/').reduce((pathname, segment, index, segments) => {
      if (!segment) {
        return pathname
      }
      if (isGroupSegment(segment)) {
        return pathname
      }
      if (segment[0] === '@') {
        return pathname
      }
      if (
        (segment === 'page' || segment === 'route') &&
        index === segments.length - 1
      ) {
        return pathname
      }
 
      return `${pathname}/${segment}`
    }, '')
  )
}

Configuration Property	Type	Default	Purpose / Behavior
`basePath`	`string`	`''`	Prefixes all application routes.
`i18n`	`object`	`null`	Enables internationalization routing.
`trailingSlash`	`boolean`	`false`	Enforces or strips trailing slashes.
`assetPrefix`	`string`	`''`	CDN or asset prefix URL for chunks.
`skipProxyUrlNormalize`	`boolean`	`false`	Bypasses automatic trailing slash normalization.

Design Choice	Benefit	Cost / Trade-off
WeakMap Locale Caching	Prevents redundant lowercasing of locale arrays while allowing GC.	Small memory overhead per unique locale array reference.
Pipelined Pathname Normalizers	Decouples concerns into single-responsibility classes.	Multiple regex checks and string slicing operations per request.
Strict App Path Normalization	Strips layout, group, and slot segments for clean URLs.	Requires manifest lookups to map public paths back to disk.