Missing Boolean.toString definition and loose valueOf definition

[Akindin]

⚙ Compilation target

ES2017

⚙ Library

lib.es5.d.ts

Missing / Incorrect Definition

interface Boolean {
    toString<T extends boolean>(this: T): `${T}`
    toString(this: Boolean): `${boolean}`
    valueOf<T extends boolean>(this: T): T
    valueOf(this: Boolean): boolean
}

TS Playground

Related issues #30225, #38347

Sample Code

const bool = true as boolean;


let a: `${boolean}` = true.toString();
let b: `${boolean}` = false.toString();
let c: `${boolean}` = bool.toString();
let d: `${boolean}` = new Boolean().toString();
let e: `${boolean}` = Boolean().toString();

let f: true = true.valueOf();
let g: false = false.valueOf();

Documentation Link

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean/toString
https://tc39.es/ecma262/multipage/fundamental-objects.html#sec-boolean.prototype.tostring
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean/valueOf
https://tc39.es/ecma262/multipage/fundamental-objects.html#sec-boolean.prototype.valueof

[jcalz]

new Boolean().toString() and true.valueOf() make me want to cry. Is there any real world example that couldn't be served equally well by just "false" or `${false}` as const or, for valueOf, just, like... true? Why would the suggested modification be a good idea for all TS code everywhere and not just merged as-needed for those who want it?

[kirkwaiblinger]

Not sure whether this constitutes any motivation to change the current definitions, but noting as a matter of interest that we do have to work around this at typescript-eslint:

https://github.com/typescript-eslint/typescript-eslint/blob/d03270fe0d8d05852d0602659e52e80531f92847/packages/eslint-plugin/src/rules/no-base-to-string.ts#L188-L194

[kirkwaiblinger]

Oh, sorry, I see that this exactly was already discussed in the referenced issue #38347