jQuery also standardizes ways of doing things between different browsers, otherwise, certain implementations would require per-browser treatment.
But as much as jQuery makes things easier for developers, the end result may not be the best. Especially in this day and age, every byte counts towards many different aspects of your website/app’s performance. Page load times, SEO, crawling performance…
A big mistake most web developers do when they start learning web technologies is to learn jQuery very quickly (because the content is abundant about jQuery tutorials and libraries) without knowing underlying technologies and what/how jQuery is helping them to do things quicker.
Why NOT jQuery?
Here are two great resources compiles the non-jQuery ways of doing things:
No jQuery Movement
Recently, the no jQuery approach became a bigger trend within the web developers communities because everybody is doing an amazing job to optimize their rich web pages and applications to score better on performance, speed.
There is a great article: https://catchjs.com/Blog/PerformanceInTheWild that analyzes a large sample set of web pages and finds jQuery being the most common dependency at half of all websites they analyzed.
With enough engineering effort and care, almost all of these pages can do what they do without jQuery and supporting libraries.