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1. DanielRosenwasser commented on Feb 20, 2021

   

   Daniel Rosenwasser (DanielRosenwasser)

   on Feb 20, 2021

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   Wenlu Wang (@Kingwl) you might be interested in this one.
2. Daniel Rosenwasser (DanielRosenwasser)

   added

   BugA bug in TypeScriptA bug in TypeScript

   Good First IssueWell scoped, documented and has the green lightWell scoped, documented and has the green light

   Help WantedYou can do thisYou can do this

   on Feb 20, 2021
3. Daniel Rosenwasser (DanielRosenwasser)

   added this to the Backlog milestone on Feb 20, 2021
4. ExE-Boss commented on Feb 20, 2021

   

   ExE Boss (ExE-Boss)

   on Feb 20, 2021

   Last edited by ExE-Boss

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   It’s not just String.raw, this applies to all tagged template literals, where the top‑level TemplateStringArray contains undefined for an unknown escape, so this should also update TemplateStringsArray:

   const taggedTemplate = (template: TemplateStringsArray, ...substitutions: unknown[]) => {
   	console.log(template, substitutions);
   }
   
   // Logs:
   // [
   // 	undefined, "bar", undefined,
   // 	raw: [ "foo\\uvar", "bar", "baz\\u" ]
   // ]
   // [ 123, 456 ]
   taggedTemplate`foo\uvar${123}bar${456}baz\u`;

   Workbench Repro

   ---

   Also, this doesn’t occur when the \u follows a substitution.
5. 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 Feb 20, 2021
6. Kingwl commented on Feb 20, 2021

   

   Wenlu Wang (Kingwl)

   on Feb 20, 2021

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   It’s not just String.raw, this applies to all tagged template literals

   Sorry I'm not 100% sure what your means.
   But seems the runtime behavior is as expected.

   

   The current problem is falsely alarm.

   Here's some context:

   • add support for Lift Template Literal Restriction #23801
   • https://tc39.github.io/proposal-template-literal-revision/

   And I have found an PR who try to fix a part of the alarm: #41030
7. ExE-Boss commented on Feb 20, 2021

   

   ExE Boss (ExE-Boss)

   on Feb 20, 2021

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   The definition of TemplateStringArray should include undefined in the top‑level index signature, which should be fixed alongside this to correctly describe the runtime behaviour as of tc39/ecma262@138c9ef.
8. Kingwl commented on Feb 20, 2021

   

   Wenlu Wang (Kingwl)

   on Feb 20, 2021

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   Ahhhh Okay. Got the point. Thanks.
9. elibarzilay commented on Jun 3, 2021

   

   Eli Barzilay (elibarzilay)

   on Jun 3, 2021

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   I think that dealing with octal escapes in all strings #396 should be done before dealing with tagged templates as an exception...
10. typescript-bot commented on Apr 14, 2022

    

    TypeScript Bot (typescript-bot)

    on Apr 14, 2022

    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 this repro running against the nightly TypeScript.

    ---

    Comment by ExE Boss (@ExE-Boss)

    ❌ Failed: -

    • Hexadecimal digit expected.

    Historical Information

    Version	Reproduction Outputs
    4.2.2, 4.3.2, 4.4.2, 4.5.2, 4.6.2	❌ Failed: - Hexadecimal digit expected.
11. bentongxyz commented on Apr 28, 2022

    

    Benjamin Tong (bentongxyz)

    on Apr 28, 2022

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    Hi, is this issue being worked on? I would like to look into this as a first issue.
12. reverofevil commented on May 22, 2022

    

    reverofevil

    on May 22, 2022

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    Almost created a duplicate to this issue.

    The proposal was here, normative section in ECMA-262 here.
13. reverofevil commented on May 22, 2022

    

    reverofevil

    on May 22, 2022

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    ExE Boss (@ExE-Boss)

    The definition of TemplateStringArray should include undefined in the top‑level index signature,

    I'm afraid such a change will break existing code. undefined is there only if a part of string template contains invalid escape characters, and this information is available in compile-time. I'd suggest replacing TemplateStringsArray with a readonly tuple of strings and undefineds, intersected with {raw: ...}. of equal-sized tuple of strings. This type should be backwards compatible.
14. Daniel Rosenwasser (DanielRosenwasser)

    closed this as completedin #51837on Mar 24, 2023
15. microsoft

    locked as resolved and limited conversation to collaborators on Oct 21, 2025