react-i18next: Unable to initialize TFunction for testing after latest version

🐛 Bug Report

Hi. I’ve initialized TFunction in my tests before i18next v22 and i18next v12, but I’m not able to do that after the upgrade.

To Reproduce

Code before the upgrade

import { TFunction } from 'react-i18next';

import { translationResources } from '../../constants';

const translation: { [key: string]: string } = translationResources.fi.translation;

const t: TFunction<'translation', undefined> = (str: string) => translation[str];

Code after the upgrade

import { TFunction } from 'i18next';

import { translationResources } from '../../constants';

const translation: { [key: string]: string } = translationResources.fi.translation;

const t: TFunction<'translation', undefined> = (str: string) => translation[str];

The error

Type '(str: string) => string' is not assignable to type 'TFunction<"translation", undefined>'.
  Type 'string' is not assignable to type 'TFunctionDetailedResult<any>'.

Expected behavior

I expect to be able to initialize TFunction

Your Environment

runtime version: node v16
i18next version: 22.0.2
os: macOS
typescript: 4.7.4

About this issue

Original URL
State: closed
Created 2 years ago
Reactions: 4
Comments: 21 (9 by maintainers)

Most upvoted comments

still relevant! had to change the import from import type { TFunction } from 'react-i18next' to import type { TFunction } from 'i18next'

HashemKhalifa on Sep 7, 2023

This works for me:

const t: TFunction = (arg: Array<string> | string): TFuncReturn<string, string, any> => {
    return typeof arg === 'string' ? arg : arg[0];
};

sternth on May 17, 2023

That’s a function overload limitation because TFunction can have multiple shapes, but it can’t determine the right one if it’s not used on the actual t function. There are a few things that I can do to remove “weight” from the TFunction and will fix your problem, I’ll keep you posted.

pedrodurek on Oct 29, 2022

Can you try with 22.0.3?

adrai on Oct 27, 2022