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Negative constant enums return number when toString is called #54992

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#55065
Closed
Negative constant enums return number when toString is called#54992
#55065
Labels
BugA bug in TypeScriptHelp WantedYou can do this
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Backlog

Description

@DustinBrett
Dustin Brett (DustinBrett)
opened on Jul 12, 2023

⏯ 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

Activity

  1. Dustin Brett (DustinBrett)
    changed the title [-]Negative numbered constant enums return typeof number when toString is called[/-] [+]Negative numbered constant enums return number when toString is called[/+] on Jul 12, 2023

  2. fatcerberus commented on Jul 12, 2023

    @fatcerberus
    Bruce Pascoe (fatcerberus)
    on Jul 12, 2023

    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.

  3. Dustin Brett (DustinBrett)
    changed the title [-]Negative numbered constant enums return number when toString is called[/-] [+]Negative constant enums return number when toString is called[/+] on Jul 12, 2023
  4. Ryan Cavanaugh (RyanCavanaugh)
    added
    BugA bug in TypeScript
    Help WantedYou can do this
    on Jul 12, 2023
  5. Ryan Cavanaugh (RyanCavanaugh)
    added this to the Backlog milestone on Jul 12, 2023

  6. RyanCavanaugh commented on Jul 12, 2023

    @RyanCavanaugh
    Ryan Cavanaugh (RyanCavanaugh)
    on Jul 12, 2023
    Member

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

  7. fatcerberus commented on Jul 12, 2023

    @fatcerberus
    Bruce Pascoe (fatcerberus)
    on Jul 12, 2023

    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.

  8. Nathan Shively-Sanders (sandersn)
    closed this as completedin #55065on Jul 31, 2023
  9. microsoft
    locked as resolved and limited conversation to collaborators on Oct 22, 2025
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