functionalscript · sergey-shandar · Aug 11, 2026 · Aug 11, 2026 · Aug 11, 2026 · Aug 11, 2026
diff --git a/AGENTS.md b/AGENTS.md
@@ -750,7 +750,7 @@ languages require. TypeScript narrows string literals precisely, so the string
    mapping (and `keyof typeof my` gives you the key type).
 
 Existing examples: `os` / `Os` and `architecture` / `Architecture` in
-`fjs/ci/common/module.f.ts`, and `actions` in `fjs/ci/config/module.f.mjs`.
+`fjs/ci/common/module.f.mjs`, and `actions` in `fjs/ci/config/module.f.mjs`.
 
 #### Write the call, not the value it computes
 

diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -20,6 +20,87 @@ history.
 
 ## Unreleased
 
+- **BREAKING CHANGES:** `fjs/bnf/module.f.ts` migrates from authored
+  TypeScript (`.f.ts`) to JSDoc-typed JavaScript (`.f.mjs`), splitting
+  its type-level API into a sibling `types.ts` — importers must use the
+  `.f.mjs` specifier for runtime values and the `types.ts` specifier
+  for types. `proof.f.ts` and `testlib.f.ts` stay TypeScript for now
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
+- **BREAKING CHANGES:** `fjs/media/nix` migrates from authored
+  TypeScript (`.f.ts`) to JSDoc-typed JavaScript (`.f.mjs`), splitting
+  the `Expression` type (and its private helper types) into a sibling
+  `types.ts` — importers must use the `.f.mjs` specifier for runtime
+  values and the `types.ts` specifier for types
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
+- **BREAKING CHANGES:** `fjs/ci/rust` migrates from authored TypeScript
+  (`.f.ts`) to JSDoc-typed JavaScript (`.f.mjs`) — importers must use
+  the `.f.mjs` specifier
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
+- **BREAKING CHANGES:** `fjs/ci/deno` migrates from authored TypeScript
+  (`.f.ts`) to JSDoc-typed JavaScript (`.f.mjs`) — importers must use
+  the `.f.mjs` specifier
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
+- **BREAKING CHANGES:** `fjs/ci/bun` migrates from authored TypeScript
+  (`.f.ts`) to JSDoc-typed JavaScript (`.f.mjs`) — importers must use
+  the `.f.mjs` specifier
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
+- **BREAKING CHANGES:** `fjs/ci/common` migrates from authored
+  TypeScript (`.f.ts`) to JSDoc-typed JavaScript (`.f.mjs`), splitting
+  its type-level API (`Os`, `Architecture`, `Image`, `Step`, `Job`,
+  `Jobs`, `GitHubAction`, `StepType`, `MetaStep`) into a sibling
+  `types.ts` — importers must use the `.f.mjs` specifier for runtime
+  values and the `types.ts` specifier for types
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
+- **BREAKING CHANGES:** `fjs/types/rtti/parse/module.f.ts` migrates from
+  authored TypeScript (`.f.ts`) to JSDoc-typed JavaScript (`.f.mjs`),
+  splitting its `Result`/`Parse` types into a sibling `types.ts` —
+  importers must use the `.f.mjs` specifier for runtime values and the
+  `types.ts` specifier for types. `proof.f.ts` stays TypeScript for
+  now: it has a type-only dependency on the not-yet-migrated `fjs/djs`
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
+- **BREAKING CHANGES:** `fjs/types/rtti/validate/module.f.ts` migrates
+  from authored TypeScript (`.f.ts`) to JSDoc-typed JavaScript
+  (`.f.mjs`) — importers must use the `.f.mjs` specifier for runtime
+  values and `fjs/types/rtti/common/types.ts` for the re-exported
+  types. `proof.f.ts` stays TypeScript for now: it has a type-only
+  dependency on the not-yet-migrated `fjs/djs`
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
+- **BREAKING CHANGES:** `fjs/types/rtti/common` migrates from authored
+  TypeScript (`.f.ts`) to JSDoc-typed JavaScript (`.f.mjs`), splitting
+  its type-level API into a sibling `types.ts` — importers must use the
+  `.f.mjs` specifier for runtime values and the `types.ts` specifier
+  for types
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
+- **BREAKING CHANGES:** `fjs/types/rtti/ts` migrates from authored
+  TypeScript (`.f.ts`) to JSDoc-typed JavaScript (`.f.mjs`), splitting
+  its `Ts<T>` type-transformer API into a sibling `types.ts` — importers
+  must use the `.f.mjs` specifier for the `printer` runtime value and
+  the `types.ts` specifier for types
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
+- **BREAKING CHANGES:** `fjs/types/rtti` migrates from authored
+  TypeScript (`.f.ts`) to JSDoc-typed JavaScript (`.f.mjs`), splitting
+  its type-level API into a sibling `types.ts` — importers must use the
+  `.f.mjs` specifier for runtime values and the `types.ts` specifier
+  for types
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
+- **BREAKING CHANGES:** `fjs/crypto/sign` migrates from authored
+  TypeScript (`.f.ts`) to JSDoc-typed JavaScript (`.f.mjs`), splitting
+  the `All` type into a sibling `types.ts` — importers must use the
+  `.f.mjs` specifier for runtime values and the `types.ts` specifier
+  for the type
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
+- **BREAKING CHANGES:** `fjs/media/html` migrates from authored
+  TypeScript (`.f.ts`) to JSDoc-typed JavaScript (`.f.mjs`), splitting
+  the `Element`/`Node` types into a sibling `types.ts` — importers must
+  use the `.f.mjs` specifier for runtime values and the `types.ts`
+  specifier for types
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
+- **BREAKING CHANGES:** `fjs/sul` migrates from authored TypeScript
+  (`.f.ts`) to JSDoc-typed JavaScript (`.f.mjs`), splitting the
+  `EncodeState`/`Encode` types into a sibling `types.ts` — importers
+  must use the `.f.mjs` specifier for runtime values and the `types.ts`
+  specifier for types
+  [#1485](https://github.com/functionalscript/functionalscript/pull/1485)
 - **BREAKING CHANGES:** `fjs/types/object`, `fjs/sul/level/literal`,
   `fjs/sul/id`, `fjs/sul/level/hash`, `fjs/types/string_set`, and the
   `module.f.ts` of `fjs/types/sorted_set` and `fjs/types/byte_set`

diff --git a/fjs/bnf/README.md b/fjs/bnf/README.md
@@ -2,7 +2,7 @@
 
 See [Backus-Naur form](https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_form).
 
-- the functional representation [./module.f.ts](./module.f.ts),
+- the functional representation [./module.f.mjs](./module.f.mjs),
 - the serializable representation [./data/](./data/),
 - symbols for multi-character tokens [./token_symbol/](./token_symbol/),
 - parser/automaton backends built over the serializable representation:

diff --git a/fjs/bnf/data/module.f.ts b/fjs/bnf/data/module.f.ts
@@ -14,10 +14,12 @@ import { stringToCodePointList } from '../../text/utf16/module.f.mjs'
 import { map, toArray } from '../../types/list/module.f.mjs'
 import {
     oneEncode,
-    type DataRule,
-    type Rule as FRule,
-    type Sequence as FSequence,
-} from '../module.f.ts'
+} from '../module.f.mjs'
+import type {
+    DataRule,
+    Rule as FRule,
+    Sequence as FSequence,
+} from '../types.ts'
 import { definedEntries } from '../../types/object/module.f.mjs'
 import type { StringMap } from '../../types/object/types.ts'
 

diff --git a/fjs/bnf/data/proof.f.ts b/fjs/bnf/data/proof.f.ts
@@ -1,7 +1,7 @@
 import { stringify } from '../../media/json/module.f.ts'
 import { identity } from '../../types/function/module.f.mjs'
 import { sort } from '../../types/object/module.f.mjs'
-import { oneEncode, option, range, rangeDecode, repeat0Plus, set } from '../module.f.ts'
+import { oneEncode, option, range, rangeDecode, repeat0Plus, set } from '../module.f.mjs'
 import { classic, deterministic } from '../testlib.f.ts'
 import { emptyTagMap, type RuleSet, toData } from './module.f.ts'
 import { assertEq } from '../../asserts/module.f.mjs'

diff --git a/fjs/bnf/descent/module.f.ts b/fjs/bnf/descent/module.f.ts
@@ -14,11 +14,12 @@
  * @module
  */
 import type { CodePoint } from '../../text/utf16/types.ts'
-import { rangeDecode, type TerminalRange } from '../module.f.ts'
+import { rangeDecode } from '../module.f.mjs'
+import type { TerminalRange } from '../types.ts'
 import { contains as rangeContains } from '../../types/range/module.f.mjs'
 import { definedEntries } from '../../types/object/module.f.mjs'
 import { emptyTagMap, toData, type Rule as DataRule, type Sequence } from '../data/module.f.ts'
-import { type Rule as FRule } from '../module.f.ts'
+import type { Rule as FRule } from '../types.ts'
 
 export type AstTag = string|true|undefined
 

diff --git a/fjs/bnf/descent/proof.f.ts b/fjs/bnf/descent/proof.f.ts
@@ -1,7 +1,7 @@
 import type { CodePoint } from '../../text/utf16/types.ts'
 import { stringToCodePointList } from '../../text/utf16/module.f.mjs'
 import { map, toArray } from '../../types/list/module.f.mjs'
-import { commaJoin0Plus, option, range, repeat0Plus, set } from '../module.f.ts'
+import { commaJoin0Plus, option, range, repeat0Plus, set } from '../module.f.mjs'
 import { deterministic } from '../testlib.f.ts'
 import { emptyTagMap, toData } from '../data/module.f.ts'
 import { descentParser, type DescentMatch, type CodePointMeta, type DescentMatchResult } from './module.f.ts'

diff --git a/fjs/bnf/ll1/module.f.ts b/fjs/bnf/ll1/module.f.ts
@@ -17,11 +17,11 @@ import type { RangeMapArray } from '../../types/range_map/types.ts'
 import { rangeMap } from '../../types/range_map/module.f.mjs'
 import { contains, set } from '../../types/string_set/module.f.mjs'
 import type { StringSet } from '../../types/string_set/types.ts'
-import { rangeDecode } from '../module.f.ts'
+import { rangeDecode } from '../module.f.mjs'
 import { definedEntries } from '../../types/object/module.f.mjs'
 import type { StringMap } from '../../types/object/types.ts'
 import { emptyTagMap, type EmptyTag, type RuleSet, toData } from '../data/module.f.ts'
-import { type Rule as FRule } from '../module.f.ts'
+import type { Rule as FRule } from '../types.ts'
 
 type DispatchRule = {
     readonly emptyTag: EmptyTag,

diff --git a/fjs/bnf/ll1/proof.f.ts b/fjs/bnf/ll1/proof.f.ts
@@ -1,6 +1,6 @@
 import { stringToCodePointList } from '../../text/utf16/module.f.mjs'
 import { toArray } from '../../types/list/module.f.mjs'
-import { commaJoin0Plus, option, range, repeat0Plus, set } from '../module.f.ts'
+import { commaJoin0Plus, option, range, repeat0Plus, set } from '../module.f.mjs'
 import { deterministic } from '../testlib.f.ts'
 import { type RuleSet, toData } from '../data/module.f.ts'
 import { dispatchMap, type MatchResult, parser, parserRuleSet } from './module.f.ts'