Feature: key prefix option

[mdjastrzebski]

Adds optional keyPrefix parameter to getFixedT function in order to allows for improved developer experience when querying deeply nested keys with common prefix.

i18next.addResource('fr', 'translation', 'very.deeply.nested.key', 'ici!');
const t = i18next.getFixedT('fr', null, 'very.deeply.nested');
const test = t('key'); // "ici!"

Original GH issue (from react-i18next): i18next/react-i18next#1359

Checklist

• only relevant code is changed (make a diff before you submit the PR)
• run tests npm run test
• tests are included

Checklist (for documentation change)

• only relevant documentation part is changed (make a diff before you submit the PR)
• motivation/reason is provided

[mdjastrzebski]

I would like to also update the docs, I'm not sure how to do it, as I haven't found docs sources in this repo.

[adrai]

probably an additional signature with second argument null is also needed?

[mdjastrzebski]

I've updated second signature to allow null value for ns argument. This should have the same effect as creating third signature getFixedT(lng: null, ns: null, keyPrefix?: string): TFunction;. @adrai wdyt?

[coveralls]

Coverage increased (+0.006%) to 93.234% when pulling 56b3b17 on mdjastrzebski:feature/key-prefix-option into e8566a0 on i18next:master.

[adrai]

The docs are here: https://github.com/i18next/i18next-gitbook/blob/master/overview/api.md#getfixedt

[adrai]

beside the typescript signature, it lgtm

[adrai]

Thank you. v20.6.0 has just been released.