Unobtrusive JavaScript
A set of principles for writing accessible, maintainable JavaScript
A library that supports unobtrusive scripting
• 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
We will cover
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.
Progressive enhancement
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
• Layer on some JavaScript (in an external script file) to apply the site’s enhanced behaviour
• 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
• One of the earliest examples of this technique, created by Aaron Boodman (now of Greasemonkey and Google Gears fame)
labels.js
• 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
<label for="search">Search</label><input type="text" id="search" name="q">
How it works
• 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
Django filter lists
Have you read our <a href="javascript:window.open( 'terms.html', 'popup', 'height=500,width=400,toolbar=no' );">terms and conditions</a>?
Bad
Have you read our <a href="#" onclick="window.open( 'terms.html', 'popup', 'height=500,width=400,toolbar=no' ); return false;" >terms and conditions</a>?
Also bad
Have you read our <a href="terms.html" onclick="window.open( 'terms.html', 'popup', 'height=500,width=400,toolbar=no' ); return false;" >terms and conditions</a>?
Better
Have you read our <a href="terms.html" onclick="window.open( this.href, 'popup', 'height=500,width=400,toolbar=no' ); return false;" >terms and conditions</a>?
Better
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
• 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
JavaScript for sidenotes
With JavaScriptwindow.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 JavaScriptwindow.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 JavaScriptwindow.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 JavaScriptwindow.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; } } }}
• 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
Problems
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; });});
• jQuery(document).ready() executes as soon as the DOM is ready
• $('a.sidenote') uses a CSS selector to traverse the DOM
• .click(function() { ... }) deals with cross-browser event handling for us
• It also avoids IE memory leaks
Advantages
Why jQuery instead of $X?
• Unlike Prototype and mooTools...
• ... it doesn’t clutter your global namespace
• Unlike YUI...
• it’s succinct
• YAHOO.util.Dom.getElementsByClassName()
• Unlike Dojo...
• ... the learning curve is hours, not days
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 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 <em>content</em>')
• $('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('<div /'>)
• els.wrapInner('<div /'>)
• els.empty()
• els.remove()
DOM construction
• var p = $('<p id="foo" />').addClass('bar');
• p.text('This is some text').css('color', 'red');
• p.appendTo(document.body);
jQuery and Microformats<ul class="restaurants"> <li class="vcard"> <h3><a class="fn org url" href="..."> Riddle & Finns</a></h3> <div class="adr"> <p class="street-address">12b Meeting House Lane</p> <p><span class="locality">Brighton</span>, <abbr class="country-name" title="United Kingdom">UK</abbr></p> <p class="postal-code">BN1 1HB</p> </div> <p>Telephone: <span class="tel">+44 (0)1273 323 008</span></p> <p class="geo">Lat/Lon: <span class="latitude">50.822563</span>, <span class="longitude">-0.140457</span> </p> </li> ...
Creating the map
jQuery(function($) { // First create a div to host the map var themap = $('<div id="themap"></div>').css({ 'width': '90%', 'height': '400px' }).insertBefore('ul.restaurants');
// Now initialise the map var mapstraction = new Mapstraction('themap','google'); mapstraction.addControls({ zoom: 'large', map_type: true });
Creating the map
jQuery(function($) { // First create a div to host the map var themap = $('<div id="themap"></div>').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( '<div class="bubble">' + hcard.html() + '</div>' ); 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( '<div class="bubble">' + hcard.html() + '</div>' ); mapstraction.addMarker(marker); });
Events
$('a:first').bind('click', function() {
$(this).css('backgroundColor' ,'red');
return false;
});
Event objects
$('a:first').click(function(ev) {
$(this).css('backgroundColor' ,'red');
ev.preventDefault();
});
Events• blur()
• change()
• click()
• dblclick()
• error()
• focus()
• keydown()
• keypress()
• keyup()
• load()
• mousedown()
• mouseover()
• mouseup()
• resize()
• scroll()
• select()
• submit()
• unload()
labels.js with jQuery
...<label class="inputHint" for="email">E-mail:</label><input id="email" type="text">...
labels.js with jQueryjQuery(function($) { $('label.inputHint').each(function() { var label = $(this); var input = $('#' + label.attr('for')); var initial = label.hide().text().replace(':', ''); input.focus(function() { input.css('color', '#000'); if (input.val() == initial) { input.val(''); } }).blur(function() { if (input.val() == '') { input.val(initial).css('color', '#aaa'); } }).css('color', '#aaa').val(initial); });});
labels.js with jQueryjQuery(function($) { $('label.inputHint').each(function() { var label = $(this); var input = $('#' + label.attr('for')); var initial = label.hide().text().replace(':', ''); input.focus(function() { input.css('color', '#000'); if (input.val() == initial) { input.val(''); } }).blur(function() { if (input.val() == '') { input.val(initial).css('color', '#aaa'); } }).css('color', '#aaa').val(initial); });});
labels.js with jQueryjQuery(function($) { $('label.inputHint').each(function() { var label = $(this); var input = $('#' + label.attr('for')); var initial = label.hide().text().replace(':', ''); input.focus(function() { input.css('color', '#000'); if (input.val() == initial) { input.val(''); } }).blur(function() { if (input.val() == '') { input.val(initial).css('color', '#aaa'); } }).css('color', '#aaa').val(initial); });});
labels.js with jQueryjQuery(function($) { $('label.inputHint').each(function() { var label = $(this); var input = $('#' + label.attr('for')); var initial = label.hide().text().replace(':', ''); input.focus(function() { input.css('color', '#000'); if (input.val() == initial) { input.val(''); } }).blur(function() { if (input.val() == '') { input.val(initial).css('color', '#aaa'); } }).css('color', '#aaa').val(initial); });});
labels.js with jQueryjQuery(function($) { $('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()
$('div.entry').css('border', '1px solid black).
find('a').css('color', 'red').end().
find('p').addClass('p-inside-entry').end();
Form help HTML
<div class="helpWrapper"> <div class="fieldWrapper"> <label for="email">E-mail address</label> <input id="email" type="text"> </div> <p class="helpText"> We promise not to spam you! </p> </div>
Form help JavaScript
jQuery(function($) { // Set up contextual help... var contextualHelp = $('<div id="contextualHelp"></div>'); contextualHelp.hide().appendTo(document.body);
Form help JavaScript
// helpArrow is a div containing the ]- thing var helpArrow = $('<div id="helpArrow"></div>').css({ 'position': 'absolute', 'left': '450px', 'top': '0px', // This changes 'height': '22px', // This changes 'width': '20px' }).hide().appendTo(document.body);
Form help JavaScript
var helpBrace = $('<div id="helpArrowBrace"></div>').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 = $('<div id="helpArrowBrace"></div>').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 = $('<div id="helpArrowBar"></div>').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');
• Complex:
• 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])
Ajax global events
• .ajaxComplete(function() { })
• .ajaxError(function() { })
• .ajaxSend(function() { })
• .ajaxStart(function() { })
• .ajaxStop(function() { })
• .ajaxSuccess(function() { })
Ajax sidenote
$('a.sidenote').one('click', function() { $('<p />').load(this.href).appendTo(document.body); // Make the link stop being a link $(this).replaceWith($(this).contents()); return false;});
Loading...
var loading = $( '<img alt="loading" src="loading.gif" />').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 = $('<div id="news_feed" class="rhsbox"></div>');news_box.html(signup.html());news_box.find('div.box').empty();var ul = $('<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 = $('<li><a href="' + link + '">' + title + '</a></li>'); 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()
$("#block").animate({
width: "+=60px",
opacity: 0.4,
fontSize: "3em",
borderWidth: "10px"
}, 1500);
You can roll your own
The shake animationfunction shake(el, callback) { el.css({'position': 'relative'}); el.animate( {left: '-10px'}, 100 ).animate( {left: '+10px'}, 100 ).animate( {left: '-10px'}, 100 ).animate( {left: '+10px'}, 100 ).animate( {left: '0px'}, 100, callback );};
The PHP$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)); } $msg = '<p class="error">Incorrect username or password.</p>';}
PHP utility functions
function is_xhr() { return (isset($_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) { $('<p class="error">Incorrect username or ' + 'password.</p>').prependTo(form). hide().slideDown(); } }); } }, 'json'); // jQuery.post(url, data, callback, type); return false; });});
shake() as a pluginjQuery.fn.shake = function(callback) { this.css({'position': 'relative'}); return this.animate( {left: '-10px'}, 100 ).animate( {left: '+10px'}, 100 ).animate( {left: '-10px'}, 100 ).animate( {left: '+10px'}, 100 ).animate( {left: '0px'}, 100, callback );};$('form').shake();$('form').shake(function() { alert('shaken!') });
Plugins
• jQuery is extensible through plugins, which can add new methods to the jQuery object
• Form: better form manipulation
• UI: drag and drop and widgets
• $('img[@src$=.png]').ifixpng()
• ... many dozens more
Logging the chain
jQuery.fn.log = function(message) { if (message) { console.log(message, this); } else { console.log(this); } return this;};
jQuery.expr[':'].second = function(a,i){return i==1;}
Extending the selector engine
$('div:second') - the second div on the page
jQuery data()
• Attaching data directly to DOM nodes can create circular references and cause memory leaks
• jQuery provides a data() method for safely attaching information
• $('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/unobtrusively-mapping-microformats-with-jquery