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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 recommend setting up tsconfig with strict mode enabled and ESLint and TypeScript ESLint rules to be fairly strict. This is a great way to learn with guard rails as it'll slap you when you try to do something which is unsafe or too loosely typed. Here's a reference ESLint config that is frequently updated with any newly released rules that fit well. This happens to be for a TypeScript React project, but you can always trim out the rules from plugins that aren't relevant for you.