Microsoft/TypeScript

Object.defineProperty(variable) does not error in `.js` files if `variable` does not exist

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#61,165 opened on Feb 12, 2025

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 (9 comments) (2 reactions) (0 assignees)TypeScript (48,455 stars) (6,726 forks)batch import
BugDomain: JavaScriptHelp Wanted

Description

🔎 Search Terms

defineProperty, cannot find namee

🕗 Version & Regression Information

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

⏯ Playground Link

https://www.typescriptlang.org/play/?noImplicitAny=false&strictFunctionTypes=false&strictPropertyInitialization=false&strictBindCallApply=false&noImplicitThis=false&noImplicitReturns=false&alwaysStrict=false&declaration=false&target=3&module=1&filetype=js&strictNullChecks=false#code/PTAEAEBcGcFoGMAWBTeBrAUCUBhRBDAOwHNlQAiAGyOPNEgHsKAVATwAdkBleAJwEt2kOv0IsuuBoQBm-WqAZD+U6PSYBbfGjL9IoZL14NeGAPIAjAFapIAOgAmyWYWQAFI516RWACnPVEABoKQnx1ZHJggG8AN3xKAFdkAC5yR2l8BMphYIB3AUh8fxSMymhkAF8ASiA

💻 Code

// javascript.js
// @ts-check
// Does not error unless in `.ts` file.
Object.defineProperty(foo, "name", { value: "default", writable: false });

🙁 Actual behavior

No error in .js files

🙂 Expected behavior

Errors in .js files with TS2304: Cannot find name 'foo'.

Additional information about the issue

Full repro: https://github.com/eps1lon/tsc-object-define-property

Contributor guide

Tech stack
typescriptjavascript
Domain
tooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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
Basic TypeScript compiler knowledgeUnderstanding of @ts check mode
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
Investigate the TypeScript compiler's handling of Object.defineProperty calls in .js files under @ts check. The missing error suggests the type checker does not treat the first argument as a reference that requires existence checking. Look in the checker.ts file for how calls to Object.defineProperty are resolved, and ensure that the argument is treated as a reference, similar to other variable references. Use the provided playground and repro repository to verify the fix.