@messageformat/fluent/lib/functions.js

Conversion & compatibility tools for using Fluent with MessageFormat 2

import { getLocaleDir } from 'messageformat/functions';
import { valueToMessageRef } from "./message-to-fluent.js";
/**
 * Build a custom function for Fluent message and term references.
 *
 * By default, {@link fluentToResource} uses this with the id `fluent:message`.
 *
 * @param res - A Map of {@link MessageFormat} instances,
 *   one for each referrable message and term.
 *   This Map may be passed in as initially empty, and later filled out by the caller.
 */
export const getMessageFunction = (res) => function message(ctx, options, input) {
    const onError = ctx.onError.bind(ctx);
    const locale = ctx.locales[0];
    const dir = ctx.dir ?? getLocaleDir(locale);
    const { msgId, msgAttr } = valueToMessageRef(input ? String(input) : '');
    const mf = res.get(msgId)?.get(msgAttr ?? '');
    if (!mf)
        throw new Error(`Message not available: ${msgId}`);
    let str;
    return {
        type: 'fluent-message',
        dir,
        selectKey(keys) {
            str ??= mf.format(options, onError);
            return keys.has(str) ? str : null;
        },
        toParts() {
            const parts = mf.formatToParts(options, onError);
            const res = dir === 'ltr' || dir === 'rtl'
                ? { type: 'fluent-message', dir, locale, parts }
                : { type: 'fluent-message', locale, parts };
            return [res];
        },
        toString: () => (str ??= mf.format(options, onError)),
        valueOf: () => (str ??= mf.format(options, onError))
    };
};