Bug in type of RegExpMatchArray/RegExpExecArray

[abramobagnara]

TypeScript Version: 2.4.0 / nightly (2.5.0-dev.201xxxxx)

Expected behavior:

From ECMA specification it should be:

interface RegExpMatchArray extends Array<string | undefined> {
    index?: number;
    input?: string;
}

interface RegExpExecArray extends Array<string | undefined> {
    index: number;
    input: string;
}

Actual behavior:

Currently is:

interface RegExpMatchArray extends Array<string> {
    index?: number;
    input?: string;
}

interface RegExpExecArray extends Array<string> {
    index: number;
    input: string;
}

[ikatyang]

Duplicate of #17053.

[jednano]

@abramobagnara, where in the ECMA specification does it have the index prop as optional (undefined)?

[abramobagnara]

@jedmao, this is not what I've written: the fix should be about array items type.