Notes about String.replace

[m-gallesio]

I am using TypeScript 5.0.4.
I have noticed the typing of String.replace seem oddly convoluted.

From lib.es5.d.ts:

interface String {
    replace(searchValue: string | RegExp, replaceValue: string): string;
    replace(searchValue: string | RegExp, replacer: (substring: string, ...args: any[]) => string): string;
}

From lib.es2015.symbol.wellknown.d.ts:

interface String {
    replace(searchValue: { [Symbol.replace](string: string, replaceValue: string): string; }, replaceValue: string): string;
    replace(searchValue: { [Symbol.replace](string: string, replacer: (substring: string, ...args: any[]) => string): string; }, replacer: (substring: string, ...args: any[]) => string): string;
}

Like the first parameter is declared as an union, I would expect the second to be the same, at least in the lib.es5 version.

Notably, this makes the following code not compile:

// The second argument is an union of replaceValue and replacer from lib.es5
const replacementSteps: ([RegExp, string | ((substring: string, ...args: any[]) => string)])[] = [
    [/(a|b)/gi, "a"],
    [/(c|d)/gi, match => match.toUpperCase()],
];

let myString = "abcdef";

for (const [searchValue, replacement] of replacementSteps)
    myString = myString.replace(searchValue, replacement); // TS2345 - the second parameter is considered invalid

By adding this into my declaration, the code works:

declare interface String {
    replace(searchValue: string | RegExp, replaceValue: string | ((substring: string, ...args: any[]) => string)): string;
}

I cannot propose a solution other than my last hack, and of course the variants with Symbol would have to be taken into account. Please consider this just a note.

See also this: microsoft/TypeScript#54223

[saschanaz]

Hi, this repository only covers non-JavaScript APIs, and issues about JavaScript ones should go microsoft/TypeScript repo.

[m-gallesio]

Understood; moving it there.