twigjs: needs_context, needs_environment

twigjs.js

// twig/factory.js
'use strict';

const Twig = require('twig');

module.exports = function () {
    Twig.extend(twig => {

        function parseParams(state, params, context) {
            if (params) {
                return twig.expression.parseAsync.call(state, params, context);
            }

            return twig.Promise.resolve(false);
        }

        // node_modules/twig/src/twig.expression.js -> type: Twig.expression.type._function
        twig.expression.extend({
            type: twig.expression.type._function,
            // Match any letter or _, then any number of letters, numbers, _ or - followed by (
            regex: /^([a-zA-Z_]\w*)\s*\(/,
            next: twig.expression.type.parameter.start,
            validate(match) {
                // Make sure this function is not a reserved word
                return match[1] && (!twig.expression.reservedWords.includes(match[1]));
            },
            transform() {
                return '(';
            },
            compile(token, stack, output) {
                const fn = token.match[1];
                token.fn = fn;
                // Cleanup token
                delete token.match;
                delete token.value;

                output.push(token);
            },
            parse(token, stack, context) {
                const state = this;
                const {fn} = token;
                let value;

                return parseParams(state, token.params, context)
                    .then(params => {
                        if (Twig.functions[fn]) {
                            // Get the function from the built-in functions
                            params = [Twig, context, ...params]; // --------------- MAIN LINE ---------------
                            value = Twig.functions[fn].apply(state, params);
                        } else if (typeof context[fn] === 'function') {
                            // Get the function from the user/context defined functions
                            value = context[fn](...params);
                        } else {
                            throw new Twig.Error(fn + ' function does not exist and is not defined in the context');
                        }

                        return value;
                    })
                    .then(result => {
                        stack.push(result);
                    });
            }
        });

    });

    Twig.extendFunction('hello', async function (Twig, context, date) {
        const data = 'Hello, {{ name }}! Today is {{ date }}.';
        const template = Twig.twig({
            data: data,
        });

        context.date = date;

        return template.renderAsync(context);
    });

    return Twig;
}

// index.js
const Twig = require('./twig/factory')();

const date = new Date().toString();
const template = `{{ hello('${date}') }}`;
const parameters = {
    name: 'Cetver'
}
Twig
    .twig({data: template})
    .renderAsync(parameters)
    .then(output => {
        console.log(output);
    });

/**
node index.js                                                                                                                                             ✘ INT  1m 52s
Hello, Cetver! Today is Thu Mar 24 2022 16:17:28 GMT+0200 (Eastern European Standard Time).
*/