Moment.js is a fantastic time & date library with lots of great features and utilities. However, if you are working on a performance sensitive web application, it might cause a huge performance overhead because of its complex APIs and large bundle size.
Memoization is a somewhat fraught topic in the React world, meaning that it's easy to go wrong with it, for example, by making memo() do nothing by passing in children to a component. The general advice is to avoid memoization until the profiler tells you to optimize, but not all use cases are general, and even in the general use case you can find tricky nuances.
Search for functional programming often results in a bunch of unreadable lingoes (for me at least), articles trying to wrap the F-word in new names like 'mappable', or people that do not understand it, but are writing tutorials either way. That isn't what I'm trying to do here. What I'm doing is learn in public. (And while we're here, check also Mostly adequate guide to FP - I.)
I think that streams are an incredibly well-designed API and have become a Swiss army knife for me. I think every web developer should strive to be familiar with them. They can be useful in a variety of situations, not only to process fetch(). Sometimes, a little stream here and there can make your life a lot easier!
Learn all you need to make a react app support Dnd interactions. Learn React Drag and drop. Learn react hooks and Polish you React Skills.
Where it may be laborious to get results through other plugins, simpleParallax.js stands out for its ease and its visual rendering. The parallax effect is directly applied to image tags, there is no need to use background images.
Hooks for fetching, caching and updating asynchronous data in React.
CSS is powerful, you can do a lot of things without JS. (That's actually an oldie, but a goodie - I.)