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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.
CSS supports a separate easing curve for each keyframe of an animation and each of these curves are cubic bezier curves so I only need to store two control points (x,y coordinates) for each frame and those determine what the curve looks like for that frame. Clicking & dragging those points just updates those x,y coordinates of the 2 control points. CSS and the web animation API actually do all the heavy lifting here as far as actually tweening those values but if you're looking for a javascript implementation of cubic bezier this one works well: https://github.com/gre/bezier-easing/blob/master/src/index.js