At ng-conf 2017, Brad Green, Engineering Director at Google, indicated that TypeScript is now an official language at Google. For developers worrying about Dart status, he clarified that both Dart and TypeScript will be in the same category.
He said, “Typescript has become allowed for unrestricted client development as of March 2017". Google is using TypeScript and Angular on TypeScript for its famous products such as Google Analytics, Firebase, and Google Cloud Platform including its critical internal tools - bug tracking, employee reviews, and product approval and launch tools. Brad also added, Google codebase has millions of lines of Dart code.