jQuery Tour

This is not meant to be a comprehensive jQuery guide, or even a tutorial, but a tour through some of its core concepts and fun and useful functions.

For more info and some great tutorials, see the jQuery site, especially

Core concept: $

  • all of jQuery lives inside a single global function
  • that function is named jQuery
  • it's also named dollar sign
  • it's a function, but it's also an object, with properties and methods of its own
$.now(); // returns the current time in msec

Core concept: Selectors

  • the parameter to the $ function is a Selector
  • a Selector is a string that matches 0 or more HTML elements
  • Selector syntax is CSS, with some extensions
    • $('a.nav[href=/home]') - selects all A elements whose class is 'nav' and whose href attribute is '/home'
  • References:

Core concept: Collections 1

  • when you call the $ function you always get back a jQuery Collection
    • even if only one element matched
    • or none
    • the docs call it a jQuery Object
  • a Collection has a length property
    • but it's not an Array

Core concept: Collections 2

  • every Collection has a gajillion methods on it
  • most of these methods return this, i.e. a pointer to the original collection
    • allows method chaining
    • some methods change the matched set
    • some methods return values, not collections, e.g. attr and html

Core concept: Collections 3

  • gotcha: some of the methods only act on the first item in the collection
    • $('a').attr('href') -- returns the href attribute of the first matching element
    • you can use each to execute a function on all items
    • or eq to reduce the set to a single item
    • $('a').eq(2).attr('href') -- returns the href attribute of the third matching element
    • $('a').last().attr('href') -- returns the href attribute of the last matching element
    • see also Filtering doc
  • gotcha: if you have an error in your selector, jQuery will not warn you
    • it will just return an empty collection

Loading jQuery

<script src="">


  • jQuery has some fun methods to animate CSS attributes
    backgroundColor: "#aa0000"
}, 1000 );

Event Listening

  • jQuery's on method
$('#hi').on('click', function() {
  • jQuery's convenience method for standard event types
$('#hi').click(function() {
  • Warning: if you call click() with no parameters, it triggers a click

return false

  • if the event listener returns false, all further processing stops
  • usually used to stop a form from actually submitting after a handled submit event

More about jQuery Event Listening

var f = function(event) {....}
  • convenience methods for standard event types

  • using on directly
$('#hi').on('click', f);
$('#ho').on('change', f);
  • on can hook many events at once
$('#hi').on('click change', f);
  • or you can use chaining for the same effect
$('#hi').on('click', f)
        .on('change', f);

Ready, Fire, Aim

jQuery has a special event that is fired when the page is "ready", i.e. the DOM hierarchy has been fully constructed.

$(document).ready(function() {
    // set up your page

It's best to put setup code in a "ready" handler rather than directly inside a <script> tag since the document might not be ready yet.

This can be abbreviated, but this might be unclear:

$(function() {
    // set up your page

"In cases where code relies on loaded assets (for example, if the dimensions of an image are required), the code should be placed in a handler for the load event instead." -