20.4. Basic jQuery Theory

At the heart of jQuery is a powerful JavaScript function called jQuery (). We use it to query our HTML page's document object model (DOM) for all elements that match a CSS selector. As a simple example, jQuery("DIV.MyClass") finds all the div elements in our DOM that have the CSS class MyClass.

jQuery () returns a jQuery-wrapped set: an instance of a jQuery object that lists the results and has many extra methods you can call to operate on those results. Most of the jQuery API consists of such methods on wrapped sets. For example, jQuery("DIV.MyClass").hide() makes all the matching div elements suddenly vanish. For brevity, jQuery provides a shorthand syntax, $(), which is exactly the same as calling jQuery(). Table 20-1 contains some further examples.