Upgrading Umbraco 7.3 with Custom Theme (KnockoutJS + AngularJS + MVC Razor) to Umbraco 13 (.NET Core) with Angular 17 – Theme & Handler Migration Guidance?

Questions
1

Hi everyone,

We are currently working on upgrading an existing Umbraco 7.3 application to Umbraco 13 (.NET Core, non-headless). The current solution has:

  • A custom theme using Theme Helper and Theme Engine
  • Frontend integration with KnockoutJS and AngularJS
  • Server-side implementation in MVC Razor, including custom JS AJAX POST calls handled via web.config-based routing/handlers

As part of the upgrade, we aim to:

  • Move to Umbraco 13 (.NET Core, non-headless)
  • Replace the frontend with Angular 17 (SPA)
  • Maintain (or migrate) the custom theme logic and handler functionality

We’re not planning to use Umbraco’s Headless or WebAPI in this case.

My questions are:

  1. Is it feasible to migrate our existing theme engine and helper-based implementation to work with Umbraco 13 in .NET Core?
  2. How can we integrate handler-like functionality in .NET Core (Umbraco 13) without WebAPI – perhaps using Razor Pages, Middleware, or another mechanism?
  3. Are there any working examples, best practices, or documentation that demonstrate this kind of migration or hybrid setup (Umbraco + Angular 17 SPA with direct handler communication)?

Any insights or examples from similar migration experiences would be greatly appreciated!

Thanks in advance!