String(number) does not return `${number}` type

[qwelias]

Bug Report

🔎 Search Terms

string constructor number type template literal

🕗 Version & Regression Information

4.2.3

⏯ Playground Link

Playground link with relevant code

💻 Code

const stringNumber: `${number}` = String(123)

🙁 Actual behavior

Error: Type 'string' is not assignable to type '${number}'.(2322)

🙂 Expected behavior

No error.

Why

String, according to ES (String(value), and ToString(argument)), uses toString method on passed in values, so ideally the fix should include only changes on Number interface, but currently it's String's def does not care about toString, so these two signature would have to be generic:

// lib.es5.d.ts
interface StringConstructor {
    new(value?: any): String;
    (value?: any): string;
}

And this one would need to be generic as well as the type of returned string would depend on the radix.

// lib.es5.d.ts
interface Number {
    toString(radix?: number): string;
}

This approach would make String easily extensible and compatible with template literal types, but I'm not sure how drastic of a change it is.

Most likely would be related to #42996

[nmain]

For now, you can augment StringConstructor in your own projects to get this effect:

interface StringConstructor {
    <T extends number>(value: T): `${T}`
}
String(32); // <32>(value: 32) => "32" (+1 overload)

The radix case seems much more difficult.

[DeepDoge]

Same issue exists with boolean and bigint as well.
Also generic overload doesn't always work in some cases, such as.

declare const foo: Promise<boolean>
foo.then(String) // gives the type Promise<string>
foo.then((foo) => String(foo)) // gives the type Promise<"true" | "false">

So currently I use this, to overcome the issue above:

interface StringConstructor {
  <T extends string | number | bigint | boolean>(value: T): `${T}`;
  (value: number): `${number}`;
  (value: bigint): `${bigint}`;
  (value: boolean): `${boolean}`;
}

Basically having normal overloads after the generic one.