Negative constant enums return number when toString is called

[DustinBrett]

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.1.6#code/MYewdgzgLgBApmArgWxgFTtAok1BvAKBmJgEEYBeGARgBoiSAhSmAWmoIF8CDRIQANnAB0AkAHMAFA2JQAngAc4IAGYwAylABOASzBSM2XMNIBKeiRjylq9Jig4UJ4VBCbd+yaYLfe4CIIiYlIyVorKau56BvaOyMKM5qHWEXZGTowubtrRXj5AA

💻 Code

const enum TestEnum {
    A = 1,
    B = -1
}

// "string",  "string" 
console.log(
    typeof String(TestEnum.A),
    typeof TestEnum.A.toString()
)

// "string",  "number" 
console.log(
    typeof String(TestEnum.B),
    typeof TestEnum.B.toString()
)

🙁 Actual behavior

Constant enums which use negative numbers will return type of number when .toString() is called.

🙂 Expected behavior

A string type should be returned

[fatcerberus]

If anyone's wondering how this happens, it's because the emit is -1 .toString() - property access has higher precedence than negation. So effectively what happens is this logs the result of typeof -(1..toString()) -- which is number.

[RyanCavanaugh]

I'm honestly shocked this has been shipping since at least 3.3, possibly forever, without getting noticed 😰

[fatcerberus]

I don’t think people generally call methods on enum values, since they’re usually just meant to be used as sentinels. Probably even fewer people still use negative values.