gettext.js

// i18n data that get's passed to jed
let DEFAULT_I18N_DATA = {
    messages: {
        en: {
            'This is a test': 'This is a test',
        },
        fr: {
            'This is a test': 'C\'est un test',
        },
        ja: {
            'This is a test': 'これはテストです',
        }
    }
}

// Our dummy Jed object, initialize this for real with `var jed = Jed()`
class Jed {
    constructor(i18ndata, locale) {
        this.options = {
            locale_data: i18ndata,
        }

        // For our dummy only...
        this.locale = locale;
    }

    // This is the main function that get's always called by Jed it seems, see
    // https://github.com/messageformat/Jed/blob/master/jed.js#L171-L225
    // for a few more details.
    // So let's use this for our proxy magic :)
    dcnpgettext(domain, context, singular_key, plural_key, val) {
        // *VERY* simplified what happens inside Jed, obviously the real
        // implementation is much more complex. for presentation only :D
        return this.options.locale_data.messages[this.locale][singular_key];
    }

    // Actually copied from Jed
    gettext(key) {
        let handler = {
            get(target, prop, receiver) {
                if (typeof prop === 'symbol') {
                    return function (value) {
                        return this.dcnpgettext.call(this, undefined, undefined, key);
                    };
                } else {
                    return Reflect.get(target, prop);
                }
            }
        };

        return new Proxy(this, handler);
    }

    // Needs to be set on `Jed` -> `Jed.setLocale = function() {...}`
    setLocale(newLocale) {
      // this.options.locale_data = require('messages/${locale}/messages.js');

      this.locale = newLocale;
    }
}

let i18n = new Jed(DEFAULT_I18N_DATA, 'en');

i18n.setLocale('en');

const myMessage = i18n.gettext('This is a test');

console.log('TRANSLATING STARTS HERE');

console.log('Translated:', myMessage);

i18n.setLocale('fr');

console.log('Translated:', myMessage);