Type definition: wrong parameter types

[lanyizi]

vue & vue-i18n version

Vue version 2.6.1, Vue-i18n version 8.15.1

Reproduction Link

https://jsfiddle.net/8svpywbg/2/

Steps to reproduce

Write this.$d(123456, { useGrouping: false });.

What is Expected?

From the documentation it looks like that when calling VueI18n's this.$n(number, key), one could also use an object as the parameter key. This object should be similar to (if not just being to an instance of) Intl.NumberFormat.

What is actually happening?

However, in Intl.NumberFormat, useGrouping's type is boolean, meanwhile this.$n() will only accept it if it's a string:

vue-i18n/types/index.d.ts

Line 182 in fc110cd

d(value: number | Date, args?: { [key: string]: string }): VueI18n.DateTimeFormatResult;

If someone write this.$n(number, { useGrouping: false }), typescript will give the following error:

No overload matches this call.
  Overload 1 of 2, '(value: number, key?: string | undefined, locale?: string | undefined): string', gave the following error.
    Argument of type '{ useGrouping: boolean; }' is not assignable to parameter of type 'string'.
  Overload 2 of 2, '(value: number, args?: { [key: string]: string; } | undefined): string', gave the following error.
    Argument of type '{ useGrouping: boolean; }' is not assignable to parameter of type '{ [key: string]: string; }'.
      Property 'useGrouping' is incompatible with index signature.
        Type 'boolean' is not assignable to type 'string'.