The ability to build modern web applications (React, Vue, Angular, Web components, Svelte etc.) in ServiceNow is a big step forward for a development community. This opens limitless possibilities and a number of options how to build ServiceNow applications.

You can build ServiceNow user interfaces using the most popular component libraries, like ant.design and blueprintjs:

Modern web development requires you to change your mental model - the way how you think about a process of building web applications. This may be a good start: https://medium.com/@pishchulin/web-development-concepts-in-servicenow-traditional-vs-modern-e7cb82bb...

And when you are ready - there is a React boilerplate which is specifically designed for ServiceNow applications: http://bit.ly/39RAVAB

The boilerplate supports all of the standard processors & loaders, lazy loading, code splitting, proxy support… and drag-n-drop deployment to ServiceNow (!)