Function replacer

packages/vite/src/node/server/middlewares/indexHtml.ts:144–197

(url: string)

): string => {
  // prefix with base (dev only, base is never relative)
  const replacer = (url: string) => {
    if (
      (url[0] === '/' && url[1] !== '/') ||
      // #3230 if some request url (localhost:3000/a/b) return to fallback html, the relative assets
      // path will add `/a/` prefix, it will caused 404.
      //
      // skip if url contains `:` as it implies a url protocol or Windows path that we don't want to replace.
      //
      // rewrite `./index.js` -> `localhost:5173/a/index.js`.
      // rewrite `../index.js` -> `localhost:5173/index.js`.
      // rewrite `relative/index.js` -> `localhost:5173/a/relative/index.js`.
      ((url[0] === '.' || isBareRelative(url)) &&
        originalUrl &&
        originalUrl !== '/' &&
        htmlPath === '/index.html')
    ) {
      url = path.posix.join(config.base, url)
    }

    let preTransformUrl: string | undefined

    if (!isClassicScriptLink && shouldPreTransform(url, config)) {
      if (url[0] === '/' && url[1] !== '/') {
        preTransformUrl = url
      } else if (url[0] === '.' || isBareRelative(url)) {
        preTransformUrl = path.posix.join(
          config.base,
          getHtmlDirnameForRelativeUrl(htmlPath),
          url,
        )
      }
    }

    if (server) {
      const mod = server.environments.client.moduleGraph.urlToModuleMap.get(
        preTransformUrl || url,
      )
      if (mod && mod.lastHMRTimestamp > 0) {
        url = injectQuery(url, `t=${mod.lastHMRTimestamp}`)
      }
    }

    if (server && preTransformUrl) {
      try {
        preTransformUrl = decodeURI(preTransformUrl)
      } catch {
        // Malformed uri. Skip pre-transform.
        return url
      }
      preTransformRequest(server, preTransformUrl, config.decodedBase)
    }

    return url
  }

  const processedUrl = useSrcSetReplacer
    ? processSrcSetSync(url, ({ url }) => replacer(url))