Should create unique symbols when creating properties on module.exports #37404

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1. RyanCavanaugh commented on Mar 16, 2020

   

   Ryan Cavanaugh (RyanCavanaugh)

   on Mar 16, 2020

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   Ron Buckton (@rbuckton) Wesley Wigham (@weswigham) what do we think should happen here?
2. Ryan Cavanaugh (RyanCavanaugh)

   added

   Needs InvestigationThis issue needs a team member to investigate its status.This issue needs a team member to investigate its status.

   on Mar 16, 2020
3. Ryan Cavanaugh (RyanCavanaugh)

   added this to the Backlog milestone on Mar 16, 2020
4. weswigham commented on Mar 16, 2020

   

   Wesley Wigham (weswigham)

   on Mar 16, 2020

   Last edited by weswigham

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   We don't make unique symbols because we see the position as mutable, ie,

   exports.customSymbol = Symbol("custom1")
   // later
   exports.customSymbol = Symbol("custom2")

   is perfectly acceptable.

   In theory, we could recognize

   Object.defineProperty(module.exports, "customSymbol", {
     writable: false,
     value: Symbol("custom")
   });

   as making the customSymbol property immutable and thus the symbol appropriately unique, but we currently do not.
5. ExE-Boss commented on Mar 16, 2020

   

   ExE Boss (ExE-Boss)

   on Mar 16, 2020

   Last edited by ExE-Boss

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   But TypeScript complains when you re‑assign a property on module.exports with:

   TS2323: Cannot redeclare exported variable 'customSymbol'.

   Also, that code looks like a bug to me, so I don’t think it should be the default.

   ---

   Also, if you do: (🔗)

   const customSymbol = Symbol("custom");
   exports.customSymbol = customSymbol;

   Then you get:

   export var customSymbol: typeof customSymbol;
   declare const customSymbol: unique symbol;
   export {};
6. weswigham commented on Mar 16, 2020

   

   Wesley Wigham (weswigham)

   on Mar 16, 2020

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   Hm. I didn't realize we issued the Cannot redeclare exported variable 'customSymbol'. error - I'm surprised we do, actually, considering there's no such limitation for cjs modules. Afaik we shouldn't be.
7. TypeScript Bot (typescript-bot)

   added

   Fix AvailableA PR has been opened for this issueA PR has been opened for this issue

   on Jul 29, 2020
8. TypeScript Bot (typescript-bot)

   added

   Has ReproThis issue has compiler-backed repros: https://aka.ms/ts-reprosThis issue has compiler-backed repros: https://aka.ms/ts-repros

   on Mar 11, 2021
9. typescript-bot commented on Mar 12, 2021

   

   TypeScript Bot (typescript-bot)

   on Mar 12, 2021

   Last edited by typescript-bot

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   👋 Hi, I'm the Repro bot. I can help narrow down and track compiler bugs across releases! This comment reflects the current state of the repro in this issue running against the nightly TypeScript.

   ---

   Issue body code block by ExE Boss (@ExE-Boss)

   ⚠️ Assertions:

   • (property) customSymbol: symbol

   Historical Information

   Issue body code block by ExE Boss (@ExE-Boss)

   Version	Reproduction Outputs
   3.8.2, 3.9.2, 4.0.2, 4.1.2, 4.2.2, Nightly	⚠️ Assertions: (property) customSymbol: symbol
10. Wesley Wigham (weswigham)

    closed this as completedin #39816on Mar 9, 2022