Object.freeze should infer narrow types on immediate properties

[dwjohnston]

Bug Report

🔎 Search Terms

Object.freeze narrow string

🕗 Version & Regression Information

Apologies, this doesn't look like a regression, but I couldn't find this in any of the FAQs. If this is a duplicate or a 'won't do' can someone point me to it?

⏯ Playground Link

Playground link with relevant code

💻 Code

type SomeObject = {
    userType: "admin" | "user"; 
}


function usesAnObject(obj: SomeObject) {

}




const theObject5 = Object.freeze({
    userType: "admin"
}); 

usesAnObject(theObject5); // Argument of type 'Readonly<{ userType: string; }>' is not assignable to parameter of type 'SomeObject'.

🙁 Actual behavior

In this code the type of the userType property is widened to string.

🙂 Expected behavior

The type should be kept as the narrower "admin" as it is not possible for that property to be reassigned.

[fatcerberus]

Use as const. The object literal is getting widened before Object.freeze() sees it.

[RyanCavanaugh]

We don't have hardcoded logic specifically for Object.freeze; it's just another function.

[jcalz]

If we had #30680 then the signature to Object.freeze() could use it; without it, there are dirty tricks that could work, but I don't think anyone wants to see them in the standard TypeScript library.

[typescript-bot]

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.