`PropertyDescriptor` (and `TypedPropertyDescriptor`) should be union of data descriptor and accessor descriptor

[lionel-rowe]

🔎 Search Terms

PropertyDescriptor, TypedPropertyDescriptor, getOwnPropertyDescriptor, getOwnPropertyDescriptor, defineProperty, defineProperties

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about PropertyDescriptor

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/MYewdgzgLgBADgJxHApgqBPAIiiwECWcUICAXDAApKrra75EkIwC8MA3jAO6FQCGAIwA2KClAQBXFABoYAcxRQAFAEpOMBEskIwMAIwwAvsYBQpgPQWYAASgQAtCgAeqYFCcIkCS9YAqABZI3BAwAEQAwvxgYCCwgnEBMBBuBABmGDD8wMC4EKSh0QAmWTAAbvzC0jCkPHxCollQEgSCklAoYU2akmBQBAC2KKYA8oIAVijuAHRFKGkEYCjUyGiYyhxGcgDkiMjbcnu0mDh4hMSkqqZAA

💻 Code

const propertyDescriptor: PropertyDescriptor = { writable: true, get() { return 1 } }

// @ts-expect-error
Object.defineProperty({}, 'prop', propertyDescriptor)

🙁 Actual behavior

No TS error, only throws "Cannot both specify accessors and a value or writable attribute" at runtime

🙂 Expected behavior

TS disallows invalid descriptors

Additional information about the issue

ECMAScript® 2026 Language Specification - 6.2.6 The Property Descriptor Specification Type (emphasis added):

Property Descriptor values may be further classified as data Property Descriptors and accessor Property Descriptors based upon the existence or use of certain fields. A data Property Descriptor is one that includes any fields named either [[Value]] or [[Writable]]. An accessor Property Descriptor is one that includes any fields named either [[Get]] or [[Set]]. Any Property Descriptor may have fields named [[Enumerable]] and [[Configurable]]. A Property Descriptor value may not be both a data Property Descriptor and an accessor Property Descriptor; however, it may be neither (in which case it is a generic Property Descriptor). A fully populated Property Descriptor is one that is either an accessor Property Descriptor or a data Property Descriptor and that has all of the corresponding fields defined in Table 3.

[lionel-rowe]

Maybe this is a dupe of #32545 and maybe that's still not currently solvable? If so can close

[MartinJohns]

This would require "negated types" or "exact types". TypeScript types are open, they allow more properties than the type definition provides.