Unobtrusive JavaScript with jQuery
Simon Willison XTech , 6th May 2008
How I learned to stop worrying and love JavaScript
Unobtrusive JavaScript
A set of principles for writing accessible, maintainable JavaScript
A library that supports unobtrusive scripting
Unobtrusive JavaScript
Theory
jQuery
Practice
We will cover
• • • •
The what and why of unobtrusive JavaScript Why use a library at all? Why pick jQuery? How jQuery handles...
• • • •
DOM manipulation Event handling Animation Ajax
Unobtrusive JavaScript
Progressive enhancement
Rather than hoping for graceful degradation, PE builds documents for the least capable or differently capable devices first, then moves on to enhance those documents with separate logic for presentation, in ways that don't place an undue burden on baseline devices but which allow a richer experience for those users with modern graphical browser software. Steven Champeon and Nick Finck, 2003
Applied to JavaScript
• Build a site that works without JavaScript • Use JavaScript to enhance that site to
provide a better user experience: easier to interact with, faster, more fun
• Start with Plain Old Semantic HTML • Layer on some CSS (in an external
stylesheet) to apply the site’s visual design external script file) to apply the site’s enhanced behaviour
• Layer on some JavaScript (in an
Surely everyone has JavaScript these days?
• There are legitimate reasons to switch it off • Some companies strip JavaScript at the
firewall
• Some people run the NoScript Firefox
extension to protect themselves from common XSS and CSRF vulnerabilities
• Many mobile devices ignore JS entirely • Screen readers DO execute JavaScript, but
accessibility issues mean that you may not want them to
The NoScript extension
Unobtrusive examples
labels.js
• One of the earliest examples of this
technique, created by Aaron Boodman (now of Greasemonkey and Google Gears fame)
How it works
• Once the page has loaded, the JavaScript: • Finds any label elements linked to a text field • Moves their text in to the associated text field • Removes them from the DOM • Sets up the event handlers to remove the
descriptive text when the field is focused
Django filter lists
• Large multi-select boxes aren't much fun • Painful to scroll through • Easy to lose track of what you have
selected
• Django's admin interface uses unobtrusive
JavaScript to improve the usability here
http://www.neighbourhoodfixit.com/
Implementing Terms and Conditions
Bad
Have you read our
terms and conditions?
Also bad
Have you read our
terms and conditions?
Better
Have you read our
terms and conditions?
Better
Have you read our
terms and conditions?
Best
Have you read our
terms and conditions?
Characteristics of unobtrusive scripts
• No in-line event handlers • All code is contained in external .js files • The site remains usable without JavaScript • Existing links and forms are repurposed • JavaScript dependent elements are
dynamically added to the page
JavaScript for sidenotes
• When the page has finished loading... • Find all links with class “sidenote” • When they’re clicked: • Launch a popup window containing the
linked page
• Don’t navigate to the page
With JavaScript
window.onload = function() { var links = document.getElementsByTagName('a'); for (var i = 0, link; link = links[i]; i++) { if (link.className == 'sidenote') { link.onclick = function() { var href = this.href; window.open(this.href, 'popup', 'height=500,width=400,toolbar=no'); return false; } } } }
With JavaScript
window.onload = function() { var links = document.getElementsByTagName('a'); for (var i = 0, link; link = links[i]; i++) { if (link.className == 'sidenote') { link.onclick = function() { var href = this.href; window.open(this.href, 'popup', 'height=500,width=400,toolbar=no'); return false; } } } }
With JavaScript
window.onload = function() { var links = document.getElementsByTagName('a'); for (var i = 0, link; link = links[i]; i++) { if (link.className == 'sidenote') { link.onclick = function() { var href = this.href; window.open(this.href, 'popup', 'height=500,width=400,toolbar=no'); return false; } } } }
With JavaScript
window.onload = function() { var links = document.getElementsByTagName('a'); for (var i = 0, link; link = links[i]; i++) { if (link.className == 'sidenote') { link.onclick = function() { var href = this.href; window.open(href, 'popup', 'height=500,width=400,toolbar=no'); return false; } } } }
Problems
Problems
• This only executes when the page has
completely loaded, including all images
• It over-writes existing load or click handlers • It can’t handle class="sidenote external" • It leaks memory in IE 6
Problems
• This only executes when the page has
completely loaded, including all images
• It over-writes existing load or click handlers • It can’t handle class="sidenote external" • It leaks memory in IE 6 • Solving these problems requires cross-
browser workarounds. That’s where libraries come in
With jQuery
jQuery(document).ready(function() { $('a.sidenote').click(function() { var href = $(this).attr('href'); window.open(href, 'popup', 'height=500,width=400,toolbar=no'); return false; }); });
With jQuery
jQuery(document).ready(function() { jQuery('a.sidenote').click(function() { var href = $(this).attr('href'); window.open(href, 'popup', 'height=500,width=400,toolbar=no'); return false; }); });
With jQuery
jQuery(document).ready(function() { jQuery('a.sidenote').click(function() { var href = jQuery(this).attr('href'); window.open(href, 'popup', 'height=500,width=400,toolbar=no'); return false; }); });
With jQuery
jQuery(document).ready(function() { jQuery('a.sidenote').click(function() { var href = jQuery(this).attr('href'); window.open(href, 'popup', 'height=500,width=400,toolbar=no'); return false; }); });
With jQuery
jQuery(function() { jQuery('a.sidenote').click(function() { var href = jQuery(this).attr('href'); window.open(href, 'popup', 'height=500,width=400,toolbar=no'); return false; }); });
With jQuery
$(function() { $('a.sidenote').click(function() { var href = $(this).attr('href'); window.open(href, 'popup', 'height=500,width=400,toolbar=no'); return false; }); });
With jQuery
jQuery(function($) { $('a.sidenote').click(function() { var href = $(this).attr('href'); window.open(href, 'popup', 'height=500,width=400,toolbar=no'); return false; }); });
Advantages
• jQuery(document).ready() executes as soon
as the DOM is ready traverse the DOM
• $('a.sidenote') uses a CSS selector to • .click(function() { ... }) deals with crossbrowser event handling for us
• It also avoids IE memory leaks
Why jQuery instead of $X?
• • •
Unlike Prototype and mooTools...
• • • •
... it doesn’t clutter your global namespace it’s succinct YAHOO.util.Dom.getElementsByClassName() ... the learning curve is hours, not days
Unlike YUI...
Unlike Dojo...
jQuery characteristics
jQuery characteristics
•
Minimal namespace impact (one symbol)
jQuery characteristics
• •
Minimal namespace impact (one symbol) Focus on the interaction between JavaScript and HTML
jQuery characteristics
• • •
Minimal namespace impact (one symbol) Focus on the interaction between JavaScript and HTML (Almost) every operation boils down to:
• •
Find some elements Do things with them
jQuery characteristics
• • • •
Minimal namespace impact (one symbol) Focus on the interaction between JavaScript and HTML (Almost) every operation boils down to:
• •
Find some elements Do things with them
Method chaining for shorter code
jQuery characteristics
• • • • •
Minimal namespace impact (one symbol) Focus on the interaction between JavaScript and HTML (Almost) every operation boils down to:
• •
Find some elements Do things with them
Method chaining for shorter code Extensible with plugins
Essential tools
Firebug extension for Firefox “Inject jQuery” bookmarklet http://icanhaz.com/xtechjs/ jQuery API docs, inc. visualjquery.com
Only one function!
• Absolutely everything* starts with a call to
the jQuery() function
• Since it’s called so often, the $ variable is set
up as an alias to jQuery
• If you’re also using another library you can
revert to the previous $ function with jQuery.noConflict();
* not entirely true
CSS selectors
jQuery('#nav') jQuery('div#intro h2') jQuery('#nav li.current a')
CSS selectors
$('#nav') $('div#intro h2') $('#nav li.current a')
CSS 2 and 3 selectors
a[rel] a[rel="friend"] a[href^="http://"] ul#nav > li li#current ~ li (li siblings that follow #current) li:first-child, li:last-child, li:nth-child(3)
Custom jQuery selectors
:first, :last, :even, :odd :header :hidden, :visible :even, :odd :input, :text, :password, :radio, :submit... :checked, :selected, :enabled, :disabled
div:has(a), div:contains(Hello), div:not(.entry)
:animated
jQuery collections
• $('div.section') returns a jQuery collection object • You can call treat it like an array
$('div.section').length = no. of matched elements $('div.section')[0] - the first div DOM element $('div.section')[1] $('div.section')[2]
jQuery collections
• $('div.section') returns a jQuery collection object • You can call methods on it:
$('div.section').size() = no. of matched elements $('div.section').each(function() { console.log(this); });
jQuery collections
• $('div.section') returns a jQuery collection object • You can call methods on it:
$('div.section').size() = no. of matched elements $('div.section').each(function(i) { console.log("Item " + i + " is ", this); });
jQuery collections
• $('div.section') returns a jQuery collection object • You can chain method calls together:
$('div.section').addClass('foo').hide(); $('div.section').each(function(i) { console.log("Item " + i + " is ", this); });
The jQuery() function
• Overloaded: behaviour depends on the type
of the arguments
• Grab elements using a selector • “Upgrade” existing DOM nodes • Create a new node from an HTML string • Schedule a function for onDomReady • Usually returns a jQuery collection object
jQuery methods
•
I’ve identified four key types of jQuery method:
• Introspectors - return data about the selected nodes • Modifiers - alter the selected nodes in some way • Navigators - traverse the DOM, change the selection • DOM modifiers - move nodes within the DOM
Introspectors
• $('div:first').attr('title') • $('div:first').html() • $('div:first').text() • $('div:first').css('color') • $('div:first').is('.entry')
Modifiers
• $('div:first').attr('title', 'The first div') • $('div:first').html('New
content') • $('div:first').text('New text content') • $('div:first').css('color', 'red')
Bulk modifiers
•
$('a:first').attr({ 'title': 'First link on the page', 'href': 'http://2008.xtech.org/' }); $('a:first').css({ 'color': 'red', 'backgroundColor': 'blue' });
•
Notice a pattern?
• $(selector).attr(name) gets • $(selector).css(name) gets • $(selector).attr(name, value) sets • $(selector).css(name, value) sets • $(selector).attr({ object }) sets in bulk • $(selector).css({ object }) sets in bulk
Style modifiers
• • • • •
$(selector).css(...) $(selector).addClass(class) $(selector).removeClass(class) $(selector).hasClass(class) $(selector).toggleClass(class)
Dimensions
• $(selector).height() • $(selector).height(200) • $(selector).width() • $(selector).width(200) • var offset = $(selector).offset() • offset.top, offset.left
Navigators - finding
• $('h1').add('h2') • $('div:first').find('a') • $('a:first').children() • $('a:first').children('em') • $('a').parent() • $('a:first').parents() • $('a:first').siblings() • $('h3').next() • $('h3:first').nextAll() • $('h3').prev() • $('h3').prevAll() • $('a:first').contents()
Navigators - filtering
• • •
$('div').eq(1) // gets second $('div').filter('.entry') $('div').filter(function(i) {
return this.className == 'foo' }
• • •
$('div').not('.entry')
$('div').slice(1, 3) // 2nd,3rd $('div').slice(-1) // last
DOM modifiers
• • • • • •
els.append(content) content.appendTo(els) els.prepend(content) content.prependTo(els) els.after(content) els.before(content)
• • • • • •
content.insertAfter(els) content.insertBefore(els) els.wrapAll('
) els.wrapInner('
) els.empty() els.remove()
DOM construction
• var p = $('
').addClass('bar'); • p.text('This is some text').css('color', 'red'); • p.appendTo(document.body);
jQuery and Microformats
Favourite restaurant list
With JavaScript enabled
jQuery and Microformats
-
12b Meeting House Lane
Brighton, UK
BN1 1HB
Telephone: +44 (0)1273 323 008
Lat/Lon: 50.822563, -0.140457
...
Creating the map
jQuery(function($) { // First create a div to host the map var themap = $('').css({ 'width': '90%', 'height': '400px' }).insertBefore('ul.restaurants'); // Now initialise the map var mapstraction = new Mapstraction('themap','google'); mapstraction.addControls({ zoom: 'large', map_type: true });
Creating the map
jQuery(function($) { // First create a div to host the map var themap = $('').css({ 'width': '90%', 'height': '400px' }).insertBefore('ul.restaurants'); // Now initialise the map var mapstraction = new Mapstraction('themap','google'); mapstraction.addControls({ zoom: 'large', map_type: true });
Displaying the map
// Show map centred on Brighton mapstraction.setCenterAndZoom( new LatLonPoint(50.8242, -0.14008), 15 // Zoom level );
Extracting the microformats
$('.vcard').each(function() { var hcard = $(this); var latitude = hcard.find('.geo .latitude').text(); var longitude = hcard.find('.geo .longitude').text(); var marker = new Marker(new LatLonPoint(latitude, longitude)); marker.setInfoBubble( '' + hcard.html() + '
' ); mapstraction.addMarker(marker); });
Extracting the microformats
$('.vcard').each(function() { var hcard = $(this); var latitude = hcard.find('.geo .latitude').text(); var longitude = hcard.find('.geo .longitude').text(); var marker = new Marker(new LatLonPoint(latitude, longitude)); marker.setInfoBubble( '' + hcard.html() + '
' ); mapstraction.addMarker(marker); });
Events
$('a:first').bind('click', function() { $(this).css('backgroundColor' ,'red'); return false; });
Events
$('a:first').click(function() { $(this).css('backgroundColor' ,'red'); return false; });
Event objects
$('a:first').click(function(ev) { $(this).css('backgroundColor' ,'red'); ev.preventDefault(); });
Triggering events
$('a:first').trigger('click');
Triggering events
$('a:first').click();
Events
• • • • • •
blur() change() click() dblclick() error() focus()
• • • • • •
keydown() keypress() keyup() load() mousedown() mouseover()
• • • • • •
mouseup() resize() scroll() select() submit() unload()
labels.js with jQuery
... ...
labels.js with jQuery
jQuery(function($) { $('label.inputHint').each(function() { var label = $(this); var input = $('#' + label.attr('for')); var initial = label.hide().text().replace(':', ''); input.focus(function() { input.css('color', '#000'); if (input.val() == initial) { input.val(''); } }).blur(function() { if (input.val() == '') { input.val(initial).css('color', '#aaa'); } }).css('color', '#aaa').val(initial); }); });
labels.js with jQuery
jQuery(function($) { $('label.inputHint').each(function() { var label = $(this); var input = $('#' + label.attr('for')); var initial = label.hide().text().replace(':', ''); input.focus(function() { input.css('color', '#000'); if (input.val() == initial) { input.val(''); } }).blur(function() { if (input.val() == '') { input.val(initial).css('color', '#aaa'); } }).css('color', '#aaa').val(initial); }); });
labels.js with jQuery
jQuery(function($) { $('label.inputHint').each(function() { var label = $(this); var input = $('#' + label.attr('for')); var initial = label.hide().text().replace(':', ''); input.focus(function() { input.css('color', '#000'); if (input.val() == initial) { input.val(''); } }).blur(function() { if (input.val() == '') { input.val(initial).css('color', '#aaa'); } }).css('color', '#aaa').val(initial); }); });
labels.js with jQuery
jQuery(function($) { $('label.inputHint').each(function() { var label = $(this); var input = $('#' + label.attr('for')); var initial = label.hide().text().replace(':', ''); input.focus(function() { input.css('color', '#000'); if (input.val() == initial) { input.val(''); } }).blur(function() { if (input.val() == '') { input.val(initial).css('color', '#aaa'); } }).css('color', '#aaa').val(initial); }); });
labels.js with jQuery
jQuery(function($) { $('label.inputHint').each(function() { var label = $(this); var input = $('#' + label.attr('for')); var initial = label.hide().text().replace(':', ''); input.focus(function() { input.css('color', '#000'); if (input.val() == initial) { input.val(''); } }).blur(function() { if (input.val() == '') { input.val(initial).css('color', '#aaa'); } }).css('color', '#aaa').val(initial); }); });
Advanced chaining
• Modified chains can be reverted using end()
$('div.entry').css('border', '1px solid black). find('a').css('color', 'red').end(). find('p').addClass('p-inside-entry').end();
Inline form help
With JavaScript enabled
Form help HTML
Form help JavaScript
jQuery(function($) { // Set up contextual help... var contextualHelp = $(''); contextualHelp.hide().appendTo(document.body);
Form help JavaScript
// helpArrow is a div containing the ]- thing var helpArrow = $('').css({ 'position': 'absolute', 'left': '450px', 'top': '0px', // This changes 'height': '22px', // This changes 'width': '20px' }).hide().appendTo(document.body);
Form help JavaScript
var helpBrace = $('').css({ 'width': '5px', 'height': '100%', 'border-right': '2px solid #ccc', 'border-bottom': '2px solid #ccc', 'border-top': '2px solid #ccc' }).appendTo(helpArrow);
Form help JavaScript
var helpBrace = $('').css({ 'width': '5px', 'height': '100%', 'border-right': '2px solid #ccc', 'border-bottom': '2px solid #ccc', 'border-top': '2px solid #ccc' }).appendTo(helpArrow);
Form help JavaScript
var helpBar = $('').css({ 'width': '15px', 'height': '0px', 'border-top': '2px solid #ccc', 'position': 'absolute', 'top': '50%', 'left': '5px' }).appendTo(helpArrow);
Form help JavaScript
function showHelp(helpWrapper, helpHtml) { // Display contextual help next to helpWrapper div var top = $(helpWrapper).offset().top; helpArrow.css('top', top + 'px'); helpArrow.height($(helpWrapper).height()).show(); contextualHelp.css('top', top + 'px').show().html(helpHtml); }
Form help JavaScript
function showHelpForField(field) { var helpWrapper = input.parents('div.helpWrapper'); var helpHtml = helpWrapper.find('p.helpText').html(); showHelp(helpWrapper, helpHtml); }
Form help JavaScript
$('div.helpWrapper').find(':input').focus(function() {
showHelpForField(this); }).end().find('p.helpText').hide();
Advanced Events
$('a:first').unbind('click'); $('a:first').unbind(); $('a:first').one('click', function() { // executes the first time the link is clicked } $('a:first').toggle(func1, func2); $('a:first').hover(func1, func2);
Custom events
function updateInbox(event, mail) { alert('New e-mail: ' + mail); } $(window).bind('mail-recieved', updateInbox) $(window).bind('mail-recieved', soundPing) $(window).trigger('mail-recieved', [mail])
Ajax
• •
Simple:
• • • • • •
jQuery('div#news').load('/news.html'); jQuery.ajax(options) - low level control jQuery.get(url, [data], [callback]) jQuery.post(url, [data], [callback], [type]) jQuery.getJSON(url, [data], [callback]) jQuery.getScript(url, [data], [callback])
Complex:
Ajax global events
• .ajaxComplete(function() { }) • .ajaxError(function() { }) • .ajaxSend(function() { }) • .ajaxStart(function() { }) • .ajaxStop(function() { }) • .ajaxSuccess(function() { })
Ajax sidenote
$('a.sidenote').one('click', function() { $('').load(this.href).appendTo(document.body); // Make the link stop being a link $(this).replaceWith($(this).contents()); return false; });
Loading...
var loading = $( '
' ).appendTo(document.body).hide() jQuery(window).ajaxStart(function() { loading.show() }); jQuery(window).ajaxStop(function() { loading.hide() });
jQuery(xml)
var signup = $('div#en_sidebar div#signup.rhsbox'); var news_box = $(''); news_box.html(signup.html()); news_box.find('div.box').empty(); var ul = $(''); var feed_url = jQuery('link[type=application/atom+xml]').attr('href'); jQuery.get(feed_url, function(xml) { var feed = jQuery(xml); feed.find('feed entry').each(function() { var title = $(this).find('title').text(); var link = $(this).find('link').attr('href'); var li = $('- ' + title + '
'); li.appendTo(ul); }); }); ul.css('text-align', 'left').appendTo(news_box.find('div.box')); news_box.insertBefore(signup);
Paste the above in to Firebug on any 2008.xtech.org page
Animation
• jQuery has built in effects:
$('h1').hide('slow'); $('h1').slideDown('fast'); $('h1').fadeOut(2000);
• Chaining automatically queues the effects:
$('h1').fadeOut(1000).slideDown()
You can roll your own
$("#block").animate({ width: "+=60px", opacity: 0.4, fontSize: "3em", borderWidth: "10px" }, 1500);
A login form that shakes its head
The shake animation
function shake(el, callback) { el.css({'position': 'relative'}); el.animate( {left: '-10px'}, 100 ).animate( {left: '+10px'}, 100 ).animate( {left: '-10px'}, 100 ).animate( {left: '+10px'}, 100 ).animate( {left: '0px'}, 100, callback ); };
The PHP
$username = isset($_POST['username']) ? $_POST['username'] : ''; $password = isset($_POST['password']) ? $_POST['password'] : ''; $msg = ''; if ($_POST) { if ($username == 'simon' && $password == 'xtech') { if (is_xhr()) { json_response(array('ok' => true, 'redirect' => 'loggedin.php')); } else { header('Location: loggedin.php'); } exit; } if (is_xhr()) { json_response(array('ok' => false)); } $msg = 'Incorrect username or password.
'; }
PHP utility functions
function is_xhr() { return (isset($_SERVER["HTTP_X_REQUESTED_WITH"]) && $_SERVER["HTTP_X_REQUESTED_WITH"] == 'XMLHttpRequest'); } function json_response($obj) { header('Content-Type: application/json'); print json_encode($obj); exit; }
The JavaScript
jQuery(function($) { $('#username').focus(); $('form').submit(function() { var form = $(this); var url = form.attr('action'); var data = form.serialize(); jQuery.post(url, data, function(json) { if (json.ok) { window.location = json.redirect; } else { ...
The JavaScript
else { $('#password').val('').focus(); shake(form, function() { if (!form.find('p.error').length) { $('Incorrect username or ' + 'password.
').prependTo(form). hide().slideDown(); } }); } }, 'json'); // jQuery.post(url, data, callback, type); return false; }); });
shake() as a plugin
jQuery.fn.shake = function(callback) { this.css({'position': 'relative'}); return this.animate( {left: '-10px'}, 100 ).animate( {left: '+10px'}, 100 ).animate( {left: '-10px'}, 100 ).animate( {left: '+10px'}, 100 ).animate( {left: '0px'}, 100, callback ); }; $('form').shake(); $('form').shake(function() { alert('shaken!') });
jQuery Plugins
Plugins
• jQuery is extensible through plugins, which • Form: better form manipulation • UI: drag and drop and widgets • $('img[@src$=.png]').ifixpng() • ... many dozens more
can add new methods to the jQuery object
Logging the chain
jQuery.fn.log = function(message) { if (message) { console.log(message, this); } else { console.log(this); } return this; };
jQuery.fn.hideLinks = function() { this.find('a[href]').hide(); return this; } $('p').hideLinks();
jQuery.fn.hideLinks = function() { this.find('a[href]').hide(); return this; } $('p').hideLinks();
jQuery.fn.hideLinks = function() { return this.find('a[href]').hide().end(); } $('p').hideLinks();
Extending the selector engine
jQuery.expr[':'].second = function(a,i){return i==1;} $('div:second') - the second div on the page
jQuery data()
• Attaching data directly to DOM nodes can
create circular references and cause memory leaks attaching information
• jQuery provides a data() method for safely • $('div:first').data('key', 'value'); • var value = $('div:first').data('key');
jQuery utilities
• • • • •
jQuery.each(object, callback) jQuery.extend(target, object) jQuery.grep(array, callback) jQuery.map(array, callback) jQuery.inArray(value, array)
• • • •
jQuery.unique(array) jQuery.makeArray(obj) jQuery.isFunction(obj) jQuery.trim(string)
Further reading
• http://jquery.com/ • http://docs.jquery.com/ • http://visualjquery.com/ - API reference • http://simonwillison.net/tags/jquery/ • http://simonwillison.net/2007/Aug/15/jquery/ • http://24ways.org/2007/unobtrusivelymapping-microformats-with-jquery