# tc39/proposal-type-annotations

ECMAScript proposal for type syntax that is erased - Stage 1

Repository: https://github.com/tc39/proposal-type-annotations
Canonical: https://ross.abutalabs.com/products/proposal-type-annotations
Homepage: https://tc39.es/proposal-type-annotations/
Language: JavaScript
License Family: other
Last push: 2025-08-27T18:02:36+00:00

## Health v2 (maintenance only)
Score: 50/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 39, release rhythm 35, longevity 100
- inputs: {"age_days": 2084, "days_push": 371, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: no_releases, no_license
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 4386, forks 52 (observed 2026-08-28T04:08:47.154570+00:00)

## What it is
A Stage 1 TC39 proposal to add erasable type annotation syntax to ECMAScript, so JavaScript engines treat type syntax as comments. It aims to let developers run TypeScript- or Flow-style code without a transpilation build step.

## Use cases
- run TypeScript code in the browser without transpiling
- remove a build step from JavaScript apps using type syntax
- standardize type annotation syntax across JS type checkers
- track the status of the types-as-comments ECMAScript proposal
- understand how engines would erase type syntax at runtime

## When to choose
- you want to follow or contribute to the standardization of type syntax in JavaScript
- you are researching how JS engines could support erasable types natively
- you are evaluating the future of TypeScript/Flow interoperability with plain JS

## When to avoid
- you need a working type checker today - use TypeScript or Flow instead
- you need a production-ready tool or library - this is only a specification proposal
- you need runtime type validation - the proposal explicitly erases types

## Facets
- artifact type: learning-resource
- maturity: experimental
- function: programming-language, type-system, compiler
- domain: programming-languages, web-development, developer-tools
- platform: cross-platform
- tags: ecmascript-proposal, tc39, typescript, type-annotations, stage-1, specification

## Member repositories
- tc39/proposal-type-annotations (main) score 50

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:08:47.154570+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-29T18:21:15.205387+00:00, confidence not recorded.
  - readme: https://github.com/tc39/proposal-type-annotations (fetched 2026-08-28T04:08:47.154570+00:00, sha 6432c2ffdd35)
  - homepage: https://tc39.es/proposal-type-annotations/ (fetched 2026-08-29T09:09:33.410353+00:00, sha c0cf505700d8)
- Data as of 2026-08-30T08:39:29.467469+00:00.