recursive_template_literals.ts

// by Simon Sturmer
// TypeScript Wizardry: Recursive Template Literals
// https://www.youtube.com/watch?v=B7ygRIQcQPE
// Creative Commons-licence

const locales = {
    en_us: {
        hello:'Hi {user}',
        greetings: {
            morning:'Good morning {user}',
            evening:'Good evening {user}'
        }
    }
}

type LocaleMap = typeof locales;

type LocaleName = keyof LocaleMap;

type Locale = LocaleMap[LocaleName];

let currentLocale: LocaleName = 'en_us';

type PathInto<T extends Record<string, any>> = keyof {
    [K in keyof T as (T[K] extends string
        ? K
        : (T[K] extends Record<string, any>
            ? `${K & string}.${PathInto<T[K]> & string}`
            : never))]: any
};

function get(object: Record<string, unknown>, path: Array<string>, index = 0): string {
    const key = path[index];
    if (key === undefined) {
        return '';
    }
    const result = object[key];
    if (result === undefined) {
        return '';
    }
    if (typeof result === 'string') {
        return result;
    }
    return get(Object(result), path, index + 1);
}

export function t(key: PathInto<Locale>): string {
    return get(locales[currentLocale], key.split('.'))
}

const translation = t('greetings.evening')