There's a fair bit of work in this area that leverages Flow type syntax, e.g:
- https://github.com/gcanti/tcomb
- https://github.com/gcanti/io-ts (for typescript)
- https://github.com/codemix/flow-runtime (i wrote this)
And another alternative is to use Design by Contract, like Eiffel:
https://github.com/codemix/babel-plugin-contracts (also me)
In Forall.js: Idris-like static types and invariant checks for JavaScriptgcanti
io-ts
TypeScript2017–2022
gcanti / io-ts
io-ts
Runtime type system for IO decoding/encoding
40Distinct people
61Mentions
0Explicit recommenders
6.8KGitHub stars
What to know before exploring
What it is
Runtime type system for IO decoding/encoding
GitHub
Where it is used
No documented product use was verified in the last source check.
What people are saying
No recommendation phrase was found in the indexed comments.
No classified warning is attached to this page. Read the discussions before treating silence as approval.
Also in these discussions
- runtypes/runtypes · linked in 7 of the same discussions
- gajus/flow-runtime · linked in 2 of the same discussions
Mentioned in the same Hacker News threads. That is not proof they are substitutes.
This week on Hacker News
Nov 8–Nov 15 UTC · Direct repository links and separately labeled related project stories. Indexed through 11/15/2026, 8:03:49 PM UTC.
No direct repository links were found in the indexed HN discussions over the past seven days. Older discussions are available below.
Mentions over time
HN mentions by year61 dated mentions
Observed mentions: 2017-04-12 02:46:33 UTC to 2022-09-23 18:51:02 UTC.
Counts come from the repository’s dated source evidence. Index cutoff: 2026-11-02 08:16:59 UTC.
View mention counts and date ranges
| Period | Start (UTC) | End (exclusive, UTC) | Mentions | Submissions | Comments |
|---|---|---|---|---|---|
| 2017 | 2017-01-01 00:00:00 UTC | 2018-01-01 00:00:00 UTC | 3 | 0 | 3 |
| 2018 | 2018-01-01 00:00:00 UTC | 2019-01-01 00:00:00 UTC | 5 | 0 | 5 |
| 2019 | 2019-01-01 00:00:00 UTC | 2020-01-01 00:00:00 UTC | 13 | 1 | 12 |
| 2020 | 2020-01-01 00:00:00 UTC | 2021-01-01 00:00:00 UTC | 23 | 0 | 23 |
| 2021 | 2021-01-01 00:00:00 UTC | 2022-01-01 00:00:00 UTC | 14 | 1 | 13 |
| 2022 | 2022-01-01 00:00:00 UTC | 2023-01-01 00:00:00 UTC | 3 | 0 | 3 |
From the project README
An excerpt from the repository, fetched Nov 13, 2026.
Read the project’s introduction
Installation
Usage
Stable features
Experimental features (version 2.2+)
Installation
To install the stable version
npm i io-ts fp-ts
Note. fp-ts is a peer dependency for io-ts
Usage
Stable features
Documentation of the main stable features (index.ts module)
Experimental modules (version 2.2+)
Experimental modules (*) are published in order to get early feedback from the community, see these tracking issues for further discussions and enhancements.
The experimental modules are independent and backward-incompatible with stable ones.
Decoder.ts module
Encoder.ts module
Codec.ts module
Eq.ts module
Schema.ts module (advanced feature)
(*) A feature tagged as Experimental is in a high state of flux, you're at risk of it changing without notice.
Read the full README on GitHubWhat Hacker News says
3 sourcesYou could write the runtime definition and extract the static types from that https://github.com/gcanti/io-ts
In TypeScript at SlackThis is a TypeScript compatible runtime type system for IO validation https://github.com/gcanti/io-ts
In TypeScript at Slack