Microsoft/TypeScript

Function implementation name must be ... (2389) when abstract method is declared again later

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#61,783 opened on May 29, 2025

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 (3 comments) (0 reactions) (0 assignees)TypeScript (6,726 forks)batch import
Domain: Error MessagesHelp WantedPossible Improvement

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Description

🔎 Search Terms

duplicate abstract function declaration, abstract method, missing implementation, abstract method overload

🕗 Version & Regression Information

  • This is the behavior in every version I tried, and I reviewed the FAQ for entries about abstract class

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/IYIwzgLgTsDGEAJYBthjAgYge2wg3gFAIkKiQzwIBmArgHawAiApigIwAUAlAFwIA3bAEsAJgG5CxUnUasUAJh78Kw+gHMC00qSgsItKPQQByABbCT2hAF9r18tDiJZzNsi59BIiYTtA

💻 Code

abstract class Foo {
    abstract func1(): void;

    func2(): string {
    // ^? Function implementation name must be 'func1'.(2389)
        return 'hi'
    }
    
    abstract func1(): void;
}

🙁 Actual behavior

TS error reported for func2, which is valid.

🙂 Expected behavior

TS error reported for func1, which has duplicated abstract declaration.

Additional information about the issue

No response

Contributor guide

Research direction
Examine the checker logic for abstract methods to understand how duplicate declarations and name mismatches are handled; trace the error reporting path for error 2389.
Tech stack
typescript
Domain
tooling
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
TypeScriptGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75