RegExpIndicesArray - Named group indices can be undefined

🔎 Search Terms

RegExpIndicesArray, Regex indices

🕗 Version & Regression Information

• This is the behaviour in every version I tried, and I reviewed the FAQ for entries about Regular Expressions

⏯ Playground Link

https://www.typescriptlang.org/play/?target=9&ts=6.0.0-dev.20260322#code/PTAEGcCcGNgWwIYEsB2A6ALuAUN6B7FcDUAc0nwFcAHUAXlGAQAoB+AHjiQBMA+AIwCUrWNzQBTAB7jozAOQJocwQEI0qbkmjjwa8lWq6A2gCIu3EwF0A3LgJESGqfTIUaRgAw3sQA

💻 Code

const group = /a(?<mid>b)?c/d.exec('ac')!.indices!.groups!["mid"];
const index = group[0];

The typing assumes that group indices are of type [number, number], but these can also be undefined

🙁 Actual behavior

typeof group === "undefined"

hence, the type system should have complained when attempting to access via index.

🙂 Expected behavior

'group' is possibly 'undefined'

...should be reported by the type system.

Additional information about the issue

https://github.com/microsoft/TypeScript/pull/61079 fixed the same issue for the outer RegExpIndicesArray itself, but not the indices array on the matched groups

Comienza con el ejemplo vinculado de Playground y compara la tipificación de los índices de grupo con el cambio externo de RegExpIndicesArray en el pull request #61079. El trabajo estará terminado cuando TypeScript informe de que el índice del grupo con nombre puede ser undefined para el código mostrado, manteniendo al mismo tiempo tipificaciones válidas para los grupos que participaron en la coincidencia.