We are looking for a way to cope with AngularJS' LTS coming to its end. We have been working for about the last 3 years on a project, written using ASP.NET Core + AngularJS 1.5.7 + Fuse theme. Altogether we've invested about 10 development years into it. The alternatives we've looked at so far were migrating to Angular2+ or React, but we expect those alternatives to be too costly (we can't afford ourselves investing ~3 development years on such a migration project). We've also considered side-by-side development – that is leaving the current code as is, and using some more advanced technology only for new features – but we couldn't find a reasonable way to implement it, and it won't actually solve the main issue we have with the LTS ending. The main issue for us with AngularJS' LTS coming to its end is the lack of security updates that come as parts of new releases (and of course we are happy to advance to a newer technology regardless).
So which technology is the simplest to migrate to, and is there some tool or library that can help us?
Moving from AngularJS to Angular is as hard as moving to any other tool because the only thing they share is the name-ish. React is my logical decision because for me it simpler due to its use of JavaScript. You don't have magic as with Angular. You use plain JavaScript to code, and things just work. The new Angular is a copy of React (mostly). And having to work with TypeScript makes things messier. You can migrate React to TypeScript, but if you have no experience, you don't need to use it. For me React is cleaner and simpler than Angular as "the new technology to use to migrate all your codebase". You can always leave your clients with the old app, and add a button to a new and shiny app in development, and ask them to try and give feedback. Doing this, you will find what's important for them, and which parts need to be prioritized instead of migrating all from a to z. It also helps your clients to learn the application step by step instead of having a sudden change to a new app that they don't totally know. Doing this you allow them to compare the old and the new one, and find their way around easily. Hope this helps you :)
I've found myself in the same scenario 2 years ago, I did the migration to Angular and the difference between both versions is huge! you are basically going to create the project from zero (again). If that is the case, I recommend React. The learning curve is smaller, it's easy to develop and maintain, and it's way better when writing specs. You could work on the migration project in parallel doing releases per feature and then replace the project when the migration is done.
