Type signature for JSON.stringify does not include undefined in the return type

[MazeChaZer]

Although calling JSON.stringify may return undefined (as documented here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#Description), it is not included in the type signature provided with TypeScript.

[MazeChaZer]

This is also true for Edge:

Values that do not have JSON representations, such as undefined, will not be converted.

https://docs.microsoft.com/en-us/scripting/javascript/reference/json-stringify-function-javascript

[mhegazy]

So we need a new overload for stringify(value: undefined, .....): undefined; ?

[MazeChaZer]

Thanks for the quick response!

That could work, please note that JSON.stringify(function() {}) also results in undefined.
Perhaps I should explain why this was a problem for me: I wrote an error handling function that would display JSON data

function showError(value: any): string {
    const json = JSON.stringify(value);
    // ...
    // Later in the code, a string function was used
    const lines = json.split('/n');
    // This is where I got the runtime exception
}

Would the overload catch this possible runtime error?

Something that would definitly work for me is a union return type that includes undefined, like so

stringify(value: any /* space, replacer, ... */): string | undefined

But of course I don't know conventions or guidelines for the type annotations very well, so this might be too broad.

[mhegazy]

PRs welcomed. You can find more information about contributing lib.d.ts fixes at https://github.com/Microsoft/TypeScript/blob/master/CONTRIBUTING.md#contributing-libdts-fixes.

[MazeChaZer]

👍 Will do

[bradleyayers]

I just discovered a production bug that this would have caught. Any updates on it @MazeChaZer?

[NN---]

@mhegazy I suggest having both return value string|undefined and additional overload for undefined|Function|symbol to catch issues at compile time.