Function preview

packages/vite/src/node/preview.ts:127–312

(
  inlineConfig: InlineConfig = {},
)

 * Starts the Vite server in preview mode, to simulate a production deployment
 */
export async function preview(
  inlineConfig: InlineConfig = {},
): Promise<PreviewServer> {
  // The preview server is a long-running, interactive process whose
  // responses cannot be replayed from a cache.
  disableCache()

  const config = await resolveConfig(
    inlineConfig,
    'serve',
    'production',
    'production',
    true,
  )

  const clientOutDir = config.environments.client.build.outDir
  const distDir = path.resolve(config.root, clientOutDir)
  if (
    !fs.existsSync(distDir) &&
    // error if no plugins implement `configurePreviewServer`
    config.plugins.every((plugin) => !plugin.configurePreviewServer) &&
    // error if called in CLI only. programmatic usage could access `httpServer`
    // and affect file serving
    process.argv[1]?.endsWith(path.normalize('bin/vite.js')) &&
    process.argv[2] === 'preview'
  ) {
    throw new Error(
      `The directory "${clientOutDir}" does not exist. Did you build your project?`,
    )
  }

  const httpsOptions = await resolveHttpsConfig(config.preview.https)
  const app = connect() as Connect.Server
  const httpServer = await resolveHttpServer(app, httpsOptions)
  setClientErrorHandler(httpServer, config.logger)

  const options = config.preview
  const logger = config.logger

  const closeHttpServer = createServerCloseFn(httpServer)

  // Promise used by `server.close()` to ensure `closeServer()` is only called once
  let closeServerPromise: Promise<void> | undefined
  const closeServer = async () => {
    teardownSIGTERMListener(closeServerAndExit)
    await closeHttpServer()
    server.resolvedUrls = null
  }

  const server: PreviewServer = {
    config,
    middlewares: app,
    httpServer,
    async close() {
      if (!closeServerPromise) {
        closeServerPromise = closeServer()
      }
      return closeServerPromise