If you've ever needed a `global` value in an express.js application using handlebars.js, then you can do this nasty hack. This allows you to write handlebars templates with variables like `{{@exphbs.data.X}}` where `X` is a property on `res.locals.globals`.

express-handlebars-globals.js

import expressHandlebars from "express-handlebars";

// setup handlebars for view templates:
const hbs = expressHandlebars.create({
  extname: ".hbs",
  helpers: { /* ... handlebars helpers */ },
});

// The express handlebars package in theory allows setting values in the
// handlebars `data` side-channel, however, the the way to set this value is via
// the options to `expressHandlebars.create` which cannot access the request
// context / request locals.
//
// As such, we need to augment the template engine, to extract the
// res.locals.globals value from the template engine's options hash
// (options._locals.globals), and set the data side channel to that value.
app.engine("hbs", function (viewPath, options, callback) {
  return hbs.engine(
    viewPath,
    {
      ...options,
      // The express handlebars package has bad types, and the `data` property
      // can only be set via setting it directly on `ConfigOptions`, not on
      // `ConfigOptions.runtimeOptions`
      // @ts-ignore
      data: options._locals.globals,
    },
    callback,
  );
});

// Setup `options._locals.globals` used above:
app.use((_req, res, next) => {
  res.locals.globals = {};
  next();
});