Problem

Object types exposed by the package were declared with type aliases. Beyond the inconsistency with the declarations already using interface, a type alias cannot be extended with module augmentation: a consumer trying to declare an extra style property gets a TS2300 Duplicate identifier error. The only workarounds were casting or widening the style objects at every call site.

Changes

Enable @typescript-eslint/consistent-type-definitions with the interface option in eslint.config.mjs. The rule sits in the shared rules block, so it applies to every package, not only core.

Convert the declarations it reports, 27 across 14 files, mostly in packages/core/src/types.ts. The conversion is mechanical and was produced with eslint --fix.

CellStyle is converted by hand: it was an intersection (CellStateStyle & { ... }), a form the rule does not flag, and it is now interface CellStyle extends CellStateStyle. Two other intersections, GraphOptions and IdentityObject, are left as type aliases.

New extension point

Applications can now declare their own style properties:

declare module '@maxgraph/core' {
  interface CellStateStyle {
    myCustomStyleProperty?: number;
  }
}

Since CellStyle extends CellStateStyle, the declaration above applies to both. CellStyle can also be augmented on its own when the property only makes sense on the style declared on a cell and not on the computed state style. The inheritance stays one-way, so such a property does not leak onto CellStateStyle.

Both directions were checked by compiling an augmentation against the generated .d.ts files, including a @ts-expect-error on the leak case.

Impact for consumers

Not a breaking change for the vast majority of consumers, and JavaScript users are not impacted at all. This is documented in the CHANGELOG under Other Changes.

The only TypeScript behavior that differs is that an interface has no implicit index signature, so these types are no longer implicitly assignable to Record<string, unknown> or to a similar index-signature type.

The single occurrence in this repository is in StyleSheet.test.ts, where the CellStyle cast passed to expect.objectContaining becomes a satisfies clause. This keeps the literal checked against CellStyle while leaving it with the index signature the matcher requires.

Validation

The full CI chain was run locally: build -w packages/core, test-check -w packages/core, 561 tests in packages/core, test -w packages/ts-support, build-all-examples.bash, build -w packages/html, check:circular-dependencies, check:npm-package and lint. Example bundle sizes are unchanged.

Note on scope

packages/website contains one .tsx file with a violation, which is fixed here. It is not covered by the CI though: the lint script glob is **/*.ts, which does not match .tsx. Extending it would surface 3 unrelated pre-existing @typescript-eslint/no-require-imports errors in that same file, so it is left for a separate change.

Summary by CodeRabbit

• Documentation

  • Updated the unreleased changelog with details about TypeScript interface usage and compatibility considerations.
  • Documented support for extending custom style properties through module augmentation.

• Developer Experience

  • Improved TypeScript API declarations by representing exported object-shaped types as interfaces.
  • Style-related types now support clearer extension patterns while preserving existing properties and behavior.
  • Added consistency checks to encourage interface-based type definitions across the codebase.