Function transform

packages/vite/src/node/plugins/importAnalysis.ts:264–875

(source, importer)

    },

    async transform(source, importer) {
      const environment = this.environment as DevEnvironment
      const ssr = environment.config.consumer === 'server'
      const moduleGraph = environment.moduleGraph

      if (canSkipImportAnalysis(importer)) {
        debug?.(colors.dim(`[skipped] ${prettifyUrl(importer, root)}`))
        return null
      }

      const msAtStart = debug ? performance.now() : 0
      await init
      let imports!: readonly ImportSpecifier[]
      let exports!: readonly ExportSpecifier[]
      source = stripBomTag(source)
      try {
        ;[imports, exports] = parseImports(source)
      } catch (_e: unknown) {
        const e = _e as EsModuleLexerParseError
        const { message, showCodeFrame } = createParseErrorInfo(
          importer,
          source,
        )
        this.error(message, showCodeFrame ? e.idx : undefined)
      }

      const depsOptimizer = environment.depsOptimizer

      // since we are already in the transform phase of the importer, it must
      // have been loaded so its entry is guaranteed in the module graph.
      const importerModule = moduleGraph.getModuleById(importer)
      if (!importerModule) {
        // This request is no longer valid. It could happen for optimized deps
        // requests. A full reload is going to request this id again.
        // Throwing an outdated error so we properly finish the request with a
        // 504 sent to the browser.
        throwOutdatedRequest(importer)
      }

      if (
        !imports.length &&
        !(this as unknown as TransformPluginContext)._addedImports
      ) {
        const prunedImports = await moduleGraph.updateModuleInfo(
          importerModule,
          new Set(),
          null,
          new Set(),
          null,
          false,
        )
        if (prunedImports) {
          handlePrunedModules(prunedImports, environment)
        }
        debug?.(
          `${timeFrom(msAtStart)} ${colors.dim(
            `[no imports] ${prettifyUrl(importer, root)}`,
          )}`,