1.2. What’s the downside?

There barely is a downside! The main arguments against using any JavaScript library have always been speed and size: some say that using a library adds too much download bloat to pages, while others claim that libraries perform poorly compared with leaner custom code. Though these arguments are worth considering, their relevance is quickly fading.

First, as far as size is concerned, jQuery is lightweight. The core jQuery library has always had a fairly small footprint: about 19kB for the basics, less than your average JPG image. Any extras your project needs (such as plugins or components from the jQuery UI library) can be added in a modular fashion, so you can easily count your bandwidth calories.