Cannot disable cache in Twing template engine (node.js, Express JS)

Question

I'm using Express JS together with Twing (node.js implementation of Twig template engine) and created a template file (index.twig.html). I'm trying to update the template without stoping and starting node.js over and over again, but it seems to be impossible.

According to https://nightlycommit.github.io/twing/api.html I can set cache to false and auto_reload to true, so that it enables templates to be recompiled whenever their content changes instead of fetching them from the cache.

const express = require('express');
const { TwingEnvironment, TwingLoaderFilesystem } = require('twing');

let loader = new TwingLoaderFilesystem('./templates');
let twing = new TwingEnvironment(loader, { // https://nightlycommit.github.io/twing/api.html
    debug: true,
    cache: false,
    auto_reload: true, //for debugging
});
const app = express();
const port = 3000;

app.use('/public', express.static('./public'));

app.get('/', (req, res) => {
    twing.render('index.twig.html', req.params).then((output) => {
        res.end(output);
    });
});

app.listen(port, () => {
    console.log(`Example app listening at http://localhost:${port}`);
});

I also thought of disabling the cache of Express JS itself with the tips from this topic: How to disable webpage caching in ExpressJS + NodeJS? Didn't help either. However, looking at the console of my browser, the HTTP response code says 200, so I don't think Express JS is the issue.

Eric MORAND · Answer 1 · 2021-10-04T23:22:15.210

See the comment here:

https://gitlab.com/nightlycommit/twing/-/issues/538

Specifically, in your case, you have to instanciate a fresh environment in your route handler, like this:

app.get('/', (req, res) => {
    let twing = new TwingEnvironment(loader, {
        debug: true
    });

    twing.render('index.twig.html', req.params).then((output) => {
        res.end(output);
    });
});

Long explanation

Twing environment uses two different layers of cache:

An internal cache. This cache can't be bypassed and can't be controled: if a compiled version of a template exists in this cache, it will always be used by the environment to load and render the template. And whenever the environment loads a template, it caches its compiled version in this internal cache. This cache has the same lifetime as the environment: whenever the environment is destroyed, it is destroyed.
An external cache, provided by the cache option. This cache can be bypassed if the template source file is more recent than the cached version and auto_reload is set to true. It has an undefined lifetime: it survives when the environment is destroyed. Said differently: it is persistent.

So, if you always want the fresh version of a template to be used, but also want to benefit from the external cache performance boost, you have to instanciate a new version of the envionrment (to get a fresh internal cache instance), set the cache option to a cache instance (or a path, to use the filesystem cache) and set auto_reload to true.

Cannot disable cache in Twing template engine (node.js, Express JS)

1 Answers1