`JSON.stringify(undefined)` incorrectly types the return value as `string`

[afgomez]

🔎 Search Terms

"JSON.stringify()"

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about "JSON.stringify()`

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/MYewdgzgLgBAZiEMC8MBSBlA8gOQHTQBOAlmAObFwCeAFAK5gAmApnKc4wJQDcAUAiAJQAhoSgQA6sSgALGgCIAkgHIAtjGCFhEGaTIxwMQgyjFVzADQw6iEDIOJ7tmfJ5A

💻 Code

const foo = JSON.stringify(undefined);
foo.startsWith("I'm crashing on runtime, uoooh oooh oooh");

🙁 Actual behavior

The foo variable is typed as string

🙂 Expected behavior

the foo variable is typed as undefined

Additional information about the issue

I think this should be relatively easy to fix with the following overload

interface JSON {
    // ...
    stringify(value: undefined, replacer?: (number | string)[] | null, space?: string | number): undefined;
}

But such a change will probably start throwing compilation errors in the wild.

[MartinJohns]

Duplicate of #18879.

[afgomez]

Oh! sorry for the noise. I only searched for JSON.stringify() in the open issues and I didn't find anything 😅.

[MartinJohns]

Searching with parentheses won't yield any result either way. Best results are with an added search modifier: JSON.stringify in:title