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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.
There are plenty of other packages that do not include type definitions. To support these situations, Microsoft also runs the DefinitelyTyped project, a GitHub repository where members of the community can submit type definitions for libraries and tools that are missing them.
I primarily use Visual Studio Code as my IDE. Among its many powerful features, VS Code comes with inbuilt TypeScript intelligence. Pop-up code completion is available for the web platform APIs as well as any third-party package that has type definitions (now, in 2022, most do).