fix(types): export MetricObjectWithValues, MetricValue and related types

[milcho0604]

Registry.getMetricsAsJSON() returns MetricObjectWithValues<MetricValue<string>>[], and the per-metric get() methods return MetricObjectWithValues<...>, but those types — along with the base MetricObject and MetricValueWithName — are not exported from index.d.ts.

As a result, consumers cannot name the return type of these public methods and have to fall back to workarounds like Awaited<ReturnType<Registry['getMetricsAsJSON']>>.

This exports the four types, consistent with the ~20 other public types already exported from the same declaration file. No behavior change, declaration-only.

• npm run compile-typescript passes.
• prettier --check index.d.ts passes.
• Verified a consumer can now import { MetricObjectWithValues, MetricValue } from 'prom-client' and annotate the getMetricsAsJSON() result.

[jdmarshall]

I think some TS unit tests would be great here.

[milcho0604]

Thanks for taking a look, and good call on wanting test coverage.

One honest caveat I ran into while adding it: because TypeScript resolves top-level types in type position even without the export keyword, a compile-only test can't actually assert the export itself — removing export from these types still type-checks. So I couldn't write a test that fails purely on the export being dropped.

What I did add to test/typescript.ts is a usage example that names the return types of getMetricsAsJSON(), getMetricsAsArray(), and Metric#get() via the now-exported type names. It exercises the intended public surface and will catch the types being removed, renamed, or reshaped, and it's compiled by tsc --project . in CI.

For context, the real value of the explicit export here is discoverability rather than a compile fix: exported symbols are what IDE auto-import suggests and what API-doc tooling (typedoc/api-extractor) surfaces, so consumers can import { MetricObjectWithValues } intentionally instead of relying on TS's non-exported-type leniency. Happy to adjust the test if you'd prefer a different shape.