Handlebars with Assemble build returning "not an own property of its parent" - express

Question

I am experiencing the dreaded not an "own property" of its parent issue when attempting to build my Handlebars project.
I have been down the rabbit hole and seen the many explanations of using #handlebars/allow-prototype-access to allow the issue to be bypassed, however it seems the project does not use a standard implementation of Handlebars...
It seems I am using something called engine-handlebars
Where I would expect to implement that allow-prototype-access change, I see the following:
app.pages('./source/pages/**/*.hbs');
app.engine('hbi', require('engine-handlebars'));
I can't fathom how I am supposed to implement the prototype access with this setup...
It seems, after a bit of trial and error, commenting lines out as I go, that the line app.pages('./source/pages/**/*.hbs'); is actually causing the issue...
When I run the project with this line in, I get the error:
Handlebars: Access has been denied to resolve the property "path" because it is not an "own property" of its parent.
You can add a runtime option to disable the check or this warning:
See https://handlebarsjs.com/api-reference/runtime-options.html#options-to-control-prototype-access for details
[10:54:49] ERROR - undefined: Cannot read property 'substring' of undefined

Answer 1

The plugin #handlebars/allow-prototype-access works by modifying the Handlebars instance.
const _Handlebars = require('handlebars');
const { allowInsecurePrototypeAccess } = require('#handlebars/allow-prototype-access');
const Handlebars = allowInsecurePrototypeAccess(_Handlebars);
Note that allowInsecurePrototypeAccess does not modify the instance in place, but creates an isolated instance via Handlebars.create() so you must use its return value.
In your case, engine-handlebars exposes the Handlebars instance in different ways depending on what version you are using.
Based on your code you provided, my guess is you are using <1.0.0, but I'll provide methods for adjusting this for all its versions.
engine-handlebars#<0.6.0
Unfortunately these versions don't expose Handlebars in any way, so if you are using this version I recommend upgrading engine-handlebars to a later version.
engine-handlebars#>=0.6.0 <1.0.0
Version 0.6.0 exposed Handlebars as a property on the exported engine function. This is then referenced throughout the library via this.Handlebars.
You can then change this before setting the app.engine() and it should work.
const _Handlebars = require('handlebars');
const { allowInsecurePrototypeAccess } = require('#handlebars/allow-prototype-access');
const engine = require('engine-handlebars');
// elsewhere...
// const app = ...
// Do this *before* setting app.engine
const insecureHandlebars = allowInsecurePrototypeAccess(_Handlebars);
engine.Handlebars = insecureHandlebars;
app.engine('hbi', engine);
engine-handlebars#>=1.0.0
For version 1.0.0 and beyond, you must pass the Handlebars instance yourself.
const Handlebars = require('handlebars');
const engine = require('engine-handlebars')(Handlebars);
Thus you don't need to set anything on engine, you just pass in the modified instance when you need it.
const _Handlebars = require('handlebars');
const { allowInsecurePrototypeAccess } = require('#handlebars/allow-prototype-access');
// elsewhere...
// const app = ...
// Do this *before* setting app.engine
const insecureHandlebars = allowInsecurePrototypeAccess(_Handlebars);
const engine = require('engine-handlebars')(insecureHandlebars);
app.engine('hbi', engine);