That’s where https://miragejs.com/ https://miragejs.com/ helps. I’ve built few fully functional prototype apps with full UI/UX without a single line of backend

That’s where https://miragejs.com/ https://miragejs.com/ helps. I’ve built few fully functional prototype apps with full UI/UX without a single line of backend code and with front-end acceptance tests. If you’re prototyping greenfield product, it’ll morph many times as you build it. Once you’re happy where it is, and you’ve stabilized on data structure (not database schemas), then just start replacing mocks withr your API calls. Acceptance tests will tell you if you’ve done it right.