`CallbackError` is incorrectly set as a `string` value

[jonkoops]

🐛 Bug Report

The value passed for CallbackError is incorrect. According to the type definition it can only be of type Error | null | undefined, but in the code it's also being passed as a string in multiple occasions.

Expected behavior

In the aforementioned cases the value should be passed as the type Error.

[adrai]

can you try with i18next v22.0.6 ?

[jonkoops]

Yeah, that works. But should the fix not be that it is always an instance of Error? Also this is a breaking change to the types as folks might not be checking for string values at this time.

For example:

const callback: MultiReadCallback = (err, data) => {
   if (err) {
     // This will now be a TypeScript error, as 'message' does not exist on type 'string'
     console.log(err.message)
   }
}

[adrai]

no, it was a string since the beginning: https://github.com/i18next/i18next-http-backend/commit/767e0b6d4946477450a3f0c07bd79812a2490cdd#diff-92bbac9a308cd5fcf9db165841f2d90ce981baddcb2b1e26cfff170929af3bd1R65

[jonkoops]

Then it's much more correct :+1: