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

🔎 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

assin it to me let me solve this it is beacuse TypeScript treats undefined variables more loosely in JavaScript files unless strict rules are applied.so i can solve this by doing easiest fix is to ensure foo is defined before usage

as a fun twist, all of these do error:

Object['defineProperty'](blah2, "name", { value: "default" })
Object.defineProperty(blah2, (void 0, "name"), { value: "default" })
Object.defineProperty(true ? blah2 : {}, "name", { value: "default" })

playground

so i'm guessing something about the exact form Object.defineProperty(obj, 'literal', { ... }) hits some special handling and causes the bug.

EDIT: it also fails if the statement is not at the top level of a module

Yeah, we treat Object.defineProperty(x, "prop") as a synthetic declaration of x.prop which (implicitly! bad!) creates the parent x declaration

Janka Uryga (@lubieowoce)

Janka Uryga (@lubieowoce) this is somewhat expected. Only the most straightforward static-ish patterns are supported by those special property assignments.

Mateusz Burzyński (@Andarist)

wht u mean to say i am wrong at that point or what Mateusz Burzyński (@Andarist)

foo gets added to file.jsGlobalAugmentations symbol table and that gets merged with globals. This mechanism was introduced in #26918

fix: workaround for TS bug in Object.defineProperty (#75944)

Nathan Shively-Sanders (@sandersn)

Nathan Shively-Sanders (@sandersn) do u have an opinion on how this should work and how file.jsGlobalAugmentations should be utilized (should they perhaps depend on checkJs or something)?

In TS7, implicit namespace creation in JS is completely gone. And I'm not sure if/when Object.defineProperty special handling will be added either. Either way, there should be an error on foo in the original example.

x.prop which (implicitly! bad!) creates the parent x declaration

why does it do that? is there an option to disable this behavior?

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Object.defineProperty(variable) does not error in `.js` files if `variable` does not exist #61165

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Object.defineProperty(variable) does not error in .js files if variable does not exist #61165

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🔎 Search Terms

🕗 Version & Regression Information

⏯ Playground Link

💻 Code

🙁 Actual behavior

🙂 Expected behavior

Additional information about the issue

Activity

mohityadav8 commented on Feb 12, 2025

lubieowoce commented on Feb 12, 2025

RyanCavanaugh commented on Feb 12, 2025

Andarist commented on Feb 13, 2025

mohityadav8 commented on Feb 13, 2025

Andarist commented on Feb 13, 2025

Andarist commented on Feb 25, 2025

sandersn commented on Apr 14, 2025

DetachHead commented on Mar 12, 2026

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Object.defineProperty(variable) does not error in `.js` files if `variable` does not exist #61165