Add prefix

[alex2844]

fastify.register(require('../index'), {
  engine: { ejs: ejs },
  ....,
  propertyName: 'mobile'
})
fastify.register(require('../index'), {
  engine: { ejs: ejs },
  ....,
  propertyName: 'desktop'
})

reply.mobile('index-for-layout.ejs', { text })
reply.desktop('index-for-layout.ejs', { text })

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[mcollina]

I would not use prefix as a name for this option as it's a common option in fastify plugins to identify a route prefix, e.g. /v1. It's best to use a different name to avoid conflicts.

Maybe propertyName, name or exposeAs.

[alex2844]

I'll be back in a few hours and fix the conflict with the current version

[mcollina]

could you please document this in the readme?

[mcollina]

lgtm

[zekth]

lgtm but what about showing the example you described in the issue?
Like having 2 different declarations with different propertynames calling different partials?

fastify.register(require('../index'), {
  engine: { ejs: ejs },
  layout: './templates/layout-mobile.hbs'
  propertyName: 'mobile'
})
fastify.register(require('../index'), {
  engine: { ejs: ejs },
  layout: './templates/layout-desktop.hbs'
  propertyName: 'desktop'
})

I think this is a revelant example to showcase this feature