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

[eps1lon]

🔎 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

[mohityadav8]

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

[lubieowoce]

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

[RyanCavanaugh]

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

[Andarist]

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

[mohityadav8]

wht u mean to say i am wrong at that point or what @Andarist

[Andarist]

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

[Andarist]

@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)?

[sandersn]

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.