All of Office 365 being rewritten in React Native and Javascript?


This tweet from a Microsoft employee seems significant to me. I’m not even going to attempt to offer any opinions. I was just quite surprised to read this and thought some of you might be interested as well.

Associated HN thread:

Comments (16)

16 responses to “All of Office 365 being rewritten in React Native and Javascript?”

  1. starkover

    Thanks for sharing. Interesting.

  2. skane2600

    Because rewriting Netscape Navigator in Java worked out so well? Microsoft doesn't have anything better to do than rewrite working applications in a new language? Sounds like more RDD (Resume Driven Development) to me.

    • longhorn

      In reply to skane2600:

      You're right about Netscape:

      Good example why rewriting a complex program is a bad idea, unless you really want to start from zero and have years at your disposal to fine-tune it.

  3. TheJoeFin

    Very interesting stuff. However I wonder what Sean Larkin means by "All of Office 365" does he mean all of the online stuff, Office Online, SharePoint, Teams, etc. or like desktop apps too? I doubt he is including the desktop apps in that, but maybe.

    EDIT: they are writing all apps in TypeScript here is the tweet

  4. jimchamplin

    So what?

    With the amount of wasted CPU time on modern PCs, nobody will notice a millisecond difference.

    OMG My hyper-fast multi-threading quad-core CPU has to execute 5% overhead...

    • TheJoeFin

      In reply to jimchamplin:

      What is your point? Because new CPUs are faster performance doesn't matter?

      • jimchamplin

        In reply to TheJoeFin:

        My point is that the overhead eventually is completely overcome by the CPU's power. If using the application never pushes the chip over say... 50%, and the JavaScript version runs at 60% tops... who cares?

        If the performance is considerably less, sure, then complain, but...


        Boxes from ten years ago are "more than capable" of running modern software. So what if there's a tiny bit of overhead in trade for WORM? Fuhgeddaboutit!

        • TheJoeFin

          In reply to jimchamplin:

          As computers become more powerful people demand more from them. My work PC frequently runs into performance limits, because I am running AutoCAD, Inventor, Outlook, OneNote, several versions of Excel, Word, File Explorer, and LOB Apps. If Microsoft announced that each instance of Excel now takes 10% more memory and CPU I would not be happy.

  5. lvthunder

    I know they want you to write all the Office Add-Ins in Javascript so it'll run everywhere.

  6. jblank46

    It's been ongoing for a while. I first noticed two years ago that OneDrive pages were written in React. It's spread to Outlook since and probably other apps too. React is awesome so I don't see why not.

  7. dcdevito

    This is terrible news. JS isn't meant for serious apps

  8. Paul Thurrott

    Everything this guy wrote is wrong, by the way.

    I covered it here:

    • TheJoeFin

      In reply to paul-thurrott:

      TypeScript is JavaScript.

      • Office Online is surely being rewritten in TypeScript because MS has been using it everywhere.
      • Skype (for Web) is being rewritten (source) without a doubt will be done in JavaScript (probably via TypeScript)
      • MS Teams was written in Angular and TypeScript
      • VS Code is written in TypeScript

      Because of the cross-platform nature of MS Office apps and the huge success of VS Code I would not be surprised if the desktop Office Applications are getting their UX rewritten in TypeScript.

      Seems to me like the vast majority of Office 365 offerings are written in JavaScript.

      • skane2600

        In reply to TheJoeFin:

        "Office Online is surely being rewritten in TypeScript because MS has been using it everywhere."

        Obviously not actually "everywhere", but even if TypeScript is used extensively by MS that would not be evidence that Office Online is being written in it.

    • aThingOrTwo

      In reply to paul-thurrott:

      I think it is more accurate to say most of it is right than everything is wrong.

      I wrote a longer comment below the article, but in summary all web technologies used to build applications (Progressive Web Apps (PWAs)/Service Workers, Electron, React, React Native) are inseparable from JavaScript because JavaScript is the language of the web.

      Skype, VSCode, Teams and Edge developer tools, Edge debug protocol all execute as JavaScript.

      The hyperbole was around office, it is not all being rewritten, but Office UI components are being migrated to use the React Native plugin for Universal Windows Platform which Microsoft has built.

      • christian.hvid

        In reply to aThingOrTwo:

        One could also argue that HTML and CSS are the languages of the web by design, while JavaScript is the language of the web by circumstance - and not necessarily forever. As technologies like WebAssembly evolve, the future companion language to HTML and CSS might just as well be C#, Swift or Kotlin - or all of them.

        As for desktop and mobile apps, web technologies are gradually supplanting native UI stacks - which is probably for the best, all things considered. It's not entirely unthinkable that even massive desktop applications like Office or Visual Studio will be rewritten using HTML and CSS at some point in the future. But I don't see JavaScript or TypeScript as a given.