[Vansh1811]

Summary

Fixes Ajv strict-mode warnings when propertyNames appears inside nested anyOf/oneOf schemas.

The validator's recursive schema conversion was applying the fjs_type transformation to propertyNames, even though it validates property keys rather than arbitrary object values. This could cause unnecessary Ajv strict-mode warnings.

Changes

• Skip the propertyNames keyword during recursive schema conversion.
• Preserve conversion of nested schemas under properties, patternProperties, and definitions.
• Add regression tests for nested combinators and user-defined fields named propertyNames.

Testing

• npm run test:unit — 588 tests passed.
• npm run test:typescript — 15 assertions passed.
• npm run lint — passed with no errors or warnings.

Closes #896

[Tony133]

Thanks for the fix, and for going further than the one-liner in the issue by handling user-defined fields named propertyNames.

I pushed a commit on top that fixes a case the new skip missed: an entry literally named propertyNames inside $defs or dependentSchemas was no longer converted, since those keywords were recursed into as schemas rather than maps of schemas. A Date reaching such an entry through a $ref then failed validation:

const build = require('fast-json-stringify')
const s = build({
  type: 'object',
  $defs: { propertyNames: { type: 'string', format: 'date-time' } },
  properties: { data: { anyOf: [{ $ref: '#/$defs/propertyNames' }, { type: 'null' }] } }
})
s({ data: new Date('2026-01-01T00:00:00Z') })
// before: TypeError: The value of '#/properties/data' does not match schema definition.
// after:  {"data":"2026-01-01T00:00:00.000Z"}

The commit adds a SCHEMA_MAP_KEYWORDS set covering all the map-valued keywords, plus a regression test. CI is green.

Merging, thanks again!