I'll do my best to give you helpful answers to some of your questions while keeping this article short, hoping you'll read it till the end.
What is jQuery?
Created in 2006, jQuery is so popular that it's still used by more than 70% of the top 10 million websites, according to W3Techs.
What are the most popular alternatives to jQuery?
The library only weighs 6KB (minified and gzipped), while jQuery weighs 30KB (minified and gzipped).
Cash has a syntax similar to jQuery but with a smaller set of features. One of the functionalities missing is Ajax, which can be implemented by using modern alternatives like Fetch API or Axios.
Even if this is not a real jQuery alternative, I think it's worth to be mentioned if you are looking for a quick way to improve the loading time of your web pages.
UmbrellaJS is another interesting library and a valuable alternative to jQuery if you don't care about compatibility with old browsers.
However, considering its last release was in 2016, at the moment of writing this article, and considering there are around 70 open issues on their GitHub page, the library is no anymore maintained.
What's the best jQuery alternative among Cash, jQuery Slim, UmbrellaJS and Zepto.js?
For example, I think these are not all alternatives to jQuery, and I think these are not all alternatives to jQuery either.
However, I don't think I will find myself in a situation where I need an alternative to jQuery, and maybe neither will you. Or maybe, we don't need jQuery at all.
In the past, you could find that almost every library was built using jQuery: Carousels, image galleries with a lightbox effect, animated popups and much more. Today is a bit different, and you might have noticed that most of these libraries moved away from jQuery or any other dependency.
Is it still worth using jQuery?
If you're building a new website and don't need to use any library that requires jQuery, then the answer is no. You can achieve everything you need using modern browser functionalities and APIs.
Is jQuery still relevant in 2023?
The short answer is yes. You can still find jQuery used in some HTML templates you download, or maybe you want to use a fancy library that depends on jQuery.
If you don't know jQuery already, then don't spend too much time learning it. A basic understanding of it will be just fine.
If you haven't done yet, I would suggest investing your time in learning React or a similar js framework. Doing that will allows you to build modern web apps with complex user interfaces.
Is React a substitute for jQuery?
I will not define React as a substitute for jQuery because they are too different in what they offer and how they work.
I hope I was able to provide you with the answers you needed. Please find some time to share this article if you like. Check also what is and what are the alternatives to jQuery Mobile.