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webpack
A bundler for javascript and friends. Packs many modules into a few bundled assets. Code Splitting allows for loading parts of the application on demand. Through "loaders", modules can be CommonJs, AMD, ES6 modules, CSS, Images, JSON, Coffeescript, LESS, ... and your custom stuff.
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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.
That much is pretty easy, the hard part is deep diving into bundlers like Webpack, which make modular programming in Javascript possible. Create React App hides some of the complexity and lets you get started writing a React app quickly, but if you're not using CRA then learning about bundling and transpiling can send you down a pretty deep rabbit hole of topics to learn.