Val Town Newsletter 3

Steve Krouse on

Founding team, assembled! Cool users continue to sign up and make cool vals. We made many small things better, and are working on making a few big things amazing. Deno, npm, omniscient debugging, and superjson hopefully soon!

If you’re new to the Val Town journey, check out our earlier blogs or just go to try out the product.

Founding team

We doubled in size (from 2 to 4) last month, so I wanted to take a moment just to gush about how lovely my colleagues are:

  • André Terron was Val Town’s first passionate user, and became Val Town’s first employee. He’s been kicking butt from Seattle since he joined in Oct. He’s pushed many of your favorite features including typescript, autocomplete, secrets,, scheduled vals, and maintained our complex runtime semantics. He’s always concerned about doing the right thing by our users, particularly around security and privacy.
  • Rodrigo Tello has been a friend since we met at when I visited Hopscotch ~7 years ago. He is a designer who is passionate about democratizing computation and fluent in Alan Kay references. He has been helping out over the past few months, and finally decided to join full time in January. He designed our beloved, simple new landing page in a couple hours, the day-of our launch, and has been quietly shipping clean, beautiful designs since.
  • Tom MacWright has been a friend and mentor to me for years. I’ve long admired his insightful blog and pragmatic technical taste that perfectly balances maintainability over the long-term while still being on the cutting-edge. I’d often DM him on Twitter for advice on which JS library to use. Now I just turn to my left 😱. It felt like he professionalized our entire codebase in his first two weeks on the job.
  • Steve Krouse (me) - Who let this guy in? I can’t say anything nice about myself, so you’ll have to read my website or my research journal and come up with your own nice things to say about me.
  • Dan, Ross (advisors) - I’d be remiss if I didn’t include Dan and Ross in the founding team. Dan instigated this whole project over the summer, and introduced me to Ross who has been advising us since the beginning. They are both very generous with their time and wisdom.

It still feels surreal how quickly the founding team has come together. Even more unlikely is that three of us live within two miles of each other in Brooklyn! We decided to go old-school with a beautiful office in the Brooklyn Navy Yard.


We’ve got some extra desks, so please reach out & stop in if you find yourself in town and want to hack on some vals in the val factory.

Cool vals 😎

We’re in a new phase of the company: y’all sign up on your own, figure things out, build stuff, read the docs, and move on with your lives, without me involved at all. Gone are the days where I had to onboard my friends by hand. New people sign up every day and make cool things, with all sorts of APIs: reddit, github (including one I made for Rodrigo), leetcode, water services, pokemon, telegram, tor, sunrise/sunset, random french products, bullet journal, porn, binance, snl, discogs, lark, and many many more in private vals… Please reach out if you make something cool or see someone else who does!


TypeScript info on hover

It may seem like a small thing, but this was one of the things I missed most from VSCode. Andre added it shockingly quickly.

Screenshot 2023-02-07 at 10.37.50 AM.png

Increased security for val tracing

Calling someone else’s val function is like calling their API. By that logic, they should be able to read any parameters you give that function. However this logic breaks down when someone uses a utility library to call an API that requires an API key. So in order to better comply with programmer’s pre-existing intuitions around how using libraries work, we now only show you tracing for evaluations where you were the person who trigger the evaluation and you are the owner of the val in question. Unfortunately this means that you won’t get tracing for vals that others run or for vals you don’t own, which will encourage folks to fork more vals to their own namespaces. We will continue to iterate on these permissions… Thanks Pat for bringing this issues to our attention!

Filters for private, public, interval vals

Screenshot 2023-02-07 at 10.39.44 AM.png

This is of Rodrigo’s first big designs at Val Town and it was implemented by Andre. Currently it only filters within your current folder, which is terribly limiting. We’re working on a new UI for val search across folders and users.

& much more!

  • Upgraded to supabase v2 JS SDK & generated types, so our codebase is more type-safe
  • Added point in time recovery to our database. Supabase missed the scheduled time, but then was able to do the upgrade without any downtime. Sorry about the confusion!
  • Added a unique index on val versions in database
  • Lots of little ui improvements, loading states, scroll bars, little optimizations and bug fixes


Deno (& npm!)

As mentioned previously, we’re switching to a more secure runtime and it increasingly looks like it’ll be Deno. And it seems that if/when it lands, we’ll get npm imports for free. (Those that are compatible with deno, anyways.) Our two most important features in one fell swoop! However this is a fairly huge rewrite, so it may take Tom couple more weeks.

Tracing/Determinism/Omniscient Debugging

One of our biggest worries in general (but particularly related to switching the runtime to Deno) is breaking user code that used to work. I’ve long dreamt of one day being able to use all past user code executions as a massive test suite that we can run new runtime code against. All we have to do is track all sources of IO (non-determinsm) and when we replay your past code, we’ll replace any calls to Date, Math.random and fetch with the values we recorded from when your code originally ran. Another upside of remembering all the things is to have a perfectly deterministic platform, so we can provide all of you with an omniscient debugging experience, that makes logging to the console unnecessary; you could always add any logs you wanted in the past retroactively! Andre has been recording your random numbers since yesterday and hopefully your fetch calls by tomorrow.

Val Permissions UI

New users are constantly confused about which of their vals are public or private. Rodrigo is working on making all this clearer in the UI.

& more!

In case you were wondering, I still do stuff. I’ve got materialized views to optimize and proxies to configure. It’s been one of my pet projects to make your fetch requests more resilient and error-free than if you ran them outside of Val Town… but more on that in another newsletter!



Currently vals are only either functions or JSON. We all desperately want many more types of vals, like Date, Set, Map, Object, Regex, Error… We’re looking very seriously at superjson. Will we ever serialize closures? A boy can dream.

Fixing mutable state bugs

The most embarrassing parts of Val Town is where we fall down on our promised semantics. We are trying to give you a collaborative JS REPL that is never turned off and that you can share with anyone in the world. As discussed above, one way this promise is betrayed is by not yet serializing enough kinds of values. But even more embarrassing is how our global @me mutable state implementation differs from your expectations of how it works in normal, single-threaded JavaScript. I won’t go into all the details here, but our friend Ross has helped me work out a locking semantics that we think will get us there, and can scale reasonably well.


You can’t rename a val in Val Town. You can just create a new val with a new name. But sometimes a rename is what you want to do. Inspired by Unison, we are moving towards a system where names are treated like metadata, so you will be able to seamlessly rename all your vals, without breaking any dependents, in your code or others’! Andre has got some great designs in place…

🙏 Tell us what you want

All of our best features have come from your requests and complaints, so keep em coming!

Happy coding!



The easiest way to subscribe to Val Town is to sign up for an account on, and then opting in to receive our newsletter as your set your username. You can also sign up via this link.

Edit this page