Introduction to jQuery

jQuery is a JavaScript library that simplified selecting and manipulating DOM elements before modern browsers standardized APIs like `querySelector`. Its entry point is the `$` function: `$("button")` selects every button on the page.

jQuery methods are chainable: `$("button").addClass("active").fadeIn();` runs both operations on the same selection, one after another, in a single line.

Even though modern vanilla JavaScript can do most of what jQuery does, huge amounts of existing production code (and many CMS themes/plugins) still depend on it — recognizing jQuery syntax is a practical skill even on new projects.