feat(types): add es-toolkit/types module with compile-time type utilities

[dayongkr]

Overview

Adds a declaration-only es-toolkit/types entrypoint for compile-time type utilities. v1 ships nine everyday helpers TypeScript lacks natively:

Type	What it does
ValueOf<T>	Union of an object's value types (value-side keyof)
Simplify<T>	Flattens an intersection/mapped type into one readable object
Merge<T, U>	Merges two objects; U overrides overlapping keys
SetOptional<T, K>	Makes specific keys optional (scoped Partial)
SetRequired<T, K>	Makes specific keys required (scoped Required)
Writable<T>	Removes readonly from all properties (inverse of Readonly)
NonEmptyArray<T>	Array with at least one element ([T, ...T[]])
DeepPartial<T>	Recursive Partial for nested object patches; plain objects, arrays/tuples (non-sparse), and Map/Set contents recurse; Date/RegExp/functions pass through
DeepReadonly<T>	Recursive Readonly for immutable state; arrays/tuples become readonly, Map/Set become ReadonlyMap/ReadonlySet

Selection rules

"Standard" = TypeScript native types (lib.*.d.ts).

1. Native already provides it → skip (Partial, Omit, NonNullable, Awaited, Uppercase, …).
2. No stricter/gap-filling variants — if something similar exists natively, use it (Except, StrictOmit, Exact skipped). Only fill what's genuinely missing.
3. Stay consistent with the native spec for related utilities (ValueOf mirrors keyof).

Provide it only when TypeScript has nothing comparable, and shape it like the native types.

Packaging

Declaration-only: publishConfig.exports exposes ./types via the types condition (no runtime default), and postbuild strips the empty JS — ships only .d.ts/.d.mts. Use with import type.

Deep utilities: where the special-casing stops

Deep utilities recurse into data containers (plain objects, arrays/tuples, Map/Set) and pass through atomic built-ins that appear in real data shapes (functions, Date, RegExp). Nothing else is special-cased (WeakMap, typed arrays, Blob, DOM types, class instances fall through to the object branch): observed demand for them is ~0, the fallout is mild, and adding a case later is non-breaking.

Tests

Co-located *.spec.ts with Vitest expectTypeOf (existing convention). 9 files, 22 tests, passing under --typecheck. Specs assert intended design decisions only (including negative cases via @ts-expect-error, e.g. sparse arrays stay illegal under DeepPartial).

Remaining TODO

• Review the test code
• Review the JSDoc descriptions
• Add the next high-priority types (by measured demand): JsonValue family → UnionToIntersection → LiteralUnion → Brand → DeepRequired

Note: the isNonEmpty guard (pairs with NonEmptyArray) belongs in predicate — separate PR.

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Project	Deployment	Actions	Updated (UTC)
es-toolkit	Ready	Preview, Comment	Jul 5, 2026 12:58pm