Object properties are allowed on const enums

[bgenia]

🔎 Search Terms

const enum Object properties constructor hasOwnProperty isPrototypeOf propertyIsEnumerable toLocaleString toString valueOf

🕗 Version & Regression Information

• This seems like a bug
• This is the behavior in every version I tried (3.3-5.3 nightly)

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.1.6#code/MYewdgzgLgBApmArgWxgITgIwE4EMYDeAvgLABQ5A9JTAIIA29MIAZjFABZwRwyjIAHAJb1euMABMYOOLgDWMbIjBQhyOOVCQQogHT0QAcwAUGHLl1boS4FBDYAlJvAQdcfUdNY8ujrggA8gDuYAAK2CACcNhQAJ5OZFZuHiZmPkIQ4SB2cVEBLAlJegap3hYCEVExsQCSEACiSOp4mKKFLsklXua6dgAyIMC4ogDKUNhCYIbt2sWeaRZ2YxNTM65zpT0AbsOIcPkJVDQAKlw8MBIgMGDZfCCCIrzG-vAAHlG2cBIJ1OhlvdwoEc-uYANoAciggPBAF1gVZYMAAIwwAC8ILw5CAA

💻 Code

const enum Bebra {}

// All of these compile and break runtime
console.log(Bebra.constructor)
console.log(Bebra.hasOwnProperty)
console.log(Bebra.isPrototypeOf)
console.log(Bebra.propertyIsEnumerable)
console.log(Bebra.toLocaleString)
console.log(Bebra.toString)
console.log(Bebra.valueOf)

// These do not compile (as expected)
Bebra.test
Bebra['test']
const c1 = Bebra

🙁 Actual behavior

TS Allows usage of Object methods on a const enum, which breaks runtime because const enums are ment to be fully erased.

🙂 Expected behavior

TS should disallow such things as it does with other properties.

Additional information about the issue

No response

[fatcerberus]

Not a duplicate, but tangentially related to #40740. In both cases there's an inherent design limitation in that TS isn't able to represent (in the type system) an object that doesn't inherit from Object.prototype.