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

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 https://github.com/microsoft/TypeScript/issues/42996

Commencez par reproduire la tâche dans le TypeScript Playground lié, puis examinez les définitions de StringConstructor et Number dans lib.es5.d.ts et lisez l’issue associée #42996. Le travail est terminé lorsqu’un comportement type-safe convenu pour String(123) et Number.toString avec des types de littéraux de modèle est atteint, avec les tests du compilateur appropriés à l’appui.