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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
I would personally look at how the devs at Elk are doing, here's the repo. The app is not "huge", but you can see that the application in production is really fast, and you have a fair amount of components rendered on screen.
Give VueUsea try, it's amazing how the library wraps common browser api around the Vue reactivity system;
Unit tests with Vitest. You can even test components and composables with it. If you're not a fan of testing components within a node environment, you can give Cypress Component testing a try;