You have spent this first part of this semester learning the nitty-gritty of JavaScript for front-end web development. This is important, so that you can write code to perform interesting tasks, monitor security, interact with users, display updated information, or collect data. You can do any of these tasks with vanilla JS; that is, plain JavaScript as understood by browsers.
However, much of the code you have written this semester, as well as implementations of many of the specifics mentioned above have already been written by other developers. This is where libraries come in. It can be considered a waste of resources for developers to end up writing a lot of the same types of functions or tasks. Why should each developer write the same thing, or one developer have to write the same thing many times, in order to do the same thing across many web apps? The answer is; they shouldn’t. It is a waste of time that could be spent solving other problems and working on other code. Libraries are ways of collecting common functions or tasks that developers need into files that can be referenced and loaded for use.
But we will focus on JQuery for one important reason. It works with HTML5 and together with HTML, CSS and JQuery, we can create some pretty amazing client-side applications.