Jazz up your JavaScript: Unobtrusive scripting with JavaScript libraries

Jazz up your JavaScriptUnobtrusive scripting with JavaScript libraries

Simon WillisonWebstock, 11th February 2008

• Unobtrusive scripting

• JavaScript libraries

• Writing unobtrusive scripts with jQuery

This tutorial

But first... let’s travel back in time to 2004

(The only photo I could find of me in 2004)

JavaScript was the ugly duckling of the web standards world

Animated snowflakes

DHTML scripts copied and pasted from dynamicdrive.com

• Unobtrusive scripting

• High quality open-source libraries

3 revolutions since 2004

• Ajax

February 2005

The quieter revolutions were just as important

Unobtrusive Scripting

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

http://www.neighbourhoodfixit.com/

• 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

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

• 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

• Clean, simple, reusable

<label for="search">Search</label><input type="text" id="search" name="q">

How it works

• An unobtrusive technique for revealing panels when links are clicked

<ul> <li><a href="#panel1" class="toggle">Panel 1</a></li> <li><a href="#panel2" class="toggle">Panel 2</a></li> <li><a href="#panel3" class="toggle">Panel 3</a></li></ul>

easytoggle.js

• When the page has loaded...

• Find all links with class="toggle" that reference an internal anchor

• Collect the elements that are referenced by those anchors

• Hide all but the first

• Set up event handlers to reveal different panels when a link is clicked

• Without JavaScript, links still jump to the right point

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

Mapping Microformats

• The hCard microformat provides a standard set of CSS classes for marking up an address

• Wouldn’t it be great if we could unobtrusively plot them on a Google Map...

• When the page loads...

• Scan through for hCards (by looking for class="vCard")

• Extract the street address and postcode for each one

• Pass it to the Google Maps geocoder to get the lat/long point

• Insert a div for the Google Map, instantiate it and add the points as markers

• Ajax is frequently used to avoid page refreshes

• So...

• Write an app that uses full page refreshes

• Use unobtrusive JS to "hijack" links and form buttons and use Ajax instead

• Jeremy Keith coined the term "Hijax" to describe this

How about Ajax?

A simple example

Have you read our <a href="javascript:window.open( 'terms.html', 'popup', 'height=500,width=400,toolbar=no' );">terms and conditions</a>?

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 still

Have you read our <a href="terms.html" class="sidenote" >terms and conditions</a>?

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

Handling events

Handling events (2)

function setupLinks() { var links = document.getElementsByTagName('a'); for (var i = 0, link; link = links[i]; i++) { if (link.className == 'sidenote') { makeLinkPopup(link); } }}

if (window.addEventListener) { window.addEventListener('load', setupLinks, false);} else if (window.attachEvent) { window.attachEvent('onload', setupLinks);}

Handling events (3)

That’s way too much nasty boilerplate

Unobtrusive challenges

• Adding events from pure script (avoiding inline script handlers) works differently between IE and other browsers

• Cancelling default actions (link navigation, form submission) also works differently

• Scripts that add behaviour need to execute as soon as the DOM is available

• All of these examples use code that runs when the window "load" event is fired

• Wait until page is loaded, then manipulate the DOM

• Problem: If the page takes a while to load (large inline images) there will be a Flash Of Unstyled Content (FOUC)

• Also, if the user clicks things before the setup code has fired they won't get the expected behaviour.

The onload problem

• A number of attempts have been made to create an onDOMReady event that fires when the DOM has been constructed but before the page has loaded

• dean.edwards.name/weblog/2006/06/again/

• Modern libraries all support this in some form

• One caveat: CSS may not have loaded, so calculated dimensions may be incorrect

onDOMReady

So we need libraries

• Writing this stuff by hand is madness

• Boilerplate code to deal with browser inconsistencies is the number one enemy of unobtrusive scripting

• Thankfully, today these are all solved problems

JavaScript Libraries

Controversial statement

• A year ago, there was a sizable debate over whether libraries were worth using at all - many people preferred to just “roll their own”

• Today, that argument is over. Libraries have won.

• (some may disagree)

“The bad news: JavaScript is broken.

The good news:It can be fixed with more JavaScript!”

Geek folk saying

JavaScript characteristics• Highly dynamic language

• Most things can be introspected

• Most things can be modified at runtime

• Functional programming, anonymous functions and closures

• Ability to modify behaviour of built-in types

• Prototypal inheritance - arguably more powerful than class-based inheritance, though much less widely understood

Modifying built-in types

var s = "This is a string";alert(s.dasherize()); // Throws an error

String.prototype.dasherize = function() { return this.toLowerCase().replace(/\s+/g, '-');}

alert(s.dasherize()); // this-is-a-string

Functional programming

function hello() { alert("hello");}

var hello = function() { alert("hello");}

(function() { alert("hello");})();

Closures

function outer() { var s = "This is a string"; function inner() { alert(s); } inner();}

Closures

function outer() { var s = "This is a string"; function inner() { alert(s); } return inner;}

var func = outer();func(); // Alerts "This is a string";

Closures

function outer(s) { function inner() { alert(s); } return inner;}

var sayHello = outer("Hello");var sayGoodbye = outer("Goodbye");sayHello();sayGoodbye();

Common library features

DOM selection

• document.getElementById shortcut

• Get elements by class name

• Get elements by CSS selector

CSS manipulation

• Manipulate and toggle classes

• Set styles (including opacity)

• Introspect applied styles

Event handling

• Cross-browser “run this function when this event happens to this element”

• Cross-browser “on DOM ready” support

• Cross-browser event introspection: where was the event targetted?

• Event triggering

• Custom events

• Cross-browser XMLHttpRequest

• Easier API for GET, POST and URL and form manipulation

• Support for Ajax formats: HTML fragments, JSON, XML

Effects and animation

• Fades, wipes and transitions

• Custom animation of any CSS property

• Automatic frame-rate management

• Easing

Widgets• Packaged widgets for things like...

• Sliders

• Calendar date pickers

• Fake “windows”

• Auto-completers

• Grids and treeviews

• Support for drag-and-drop

Language tools

• Iteration over objects and arrays

• Utilities for managing prototypal inheritance

• Traditional class-based inheritance

• Tools for managing scope and callbacks

• Dynamic code loading

Array manipulation

for (var i = 0; i < arr.length; i++) { var item = arr[i]; // process item}

forEach(arr, function(item) { // process item});

doubles = map(arr, function(i) { return i * 2 });evens = filter(arr, function(i) { return i % 2 == 0 });

Other characteristics• Do they modify built in types?

• Global namespace impact

• Library size and componentization

• Support for accessibility (esp. for widgets)

• Browser support

• Documentation

• Community

The big five

• The Yahoo! User Interface Library

• Prototype (and Script.aculo.us)

• The Dojo Toolkit

• mooTools

• jQuery

The Example

• A login form that shakes its head at you

• Standard POST login form, unobtrusively upgraded to use Ajax and shake if the password is incorrect

• Behind the scenes, JSON is used for the reply to say if the password was correct or not

Simple login JSON API

• Responds to the same POST as the regular form, but looks for X-Requested-With: XMLHttpRequest header

• If login fails, returns

{"ok":false}

• If login succeeds, returns

{"ok": true, "redirect": "loggedin.php"}

The Yahoo! User Interface Library

dom event connection

animation dragdrop

utilities

controls (aka widgets)

autocomplete calendar

menu slider treeview

container

YAHOO.util.Event.onDOMReady(function() { var $E = YAHOO.util.Event; var $D = YAHOO.util.Dom; var $C = YAHOO.util.Connect; var query = YAHOO.util.Selector.query; $D.get('username').focus(); var form = query('form')[0];

$E.on(form, 'submit', function(ev) { $E.preventDefault(ev); var url = form.action; $C.setForm(form); $C.asyncRequest( 'POST', url, { success: function() { ... } } );});

success: function(response) { var json = eval('(' + response.responseText + ')'); if (json.ok) { window.location = json.redirect; } else { $D.get('password').value = ''; $D.get('password').focus(); shake(form, function() { if (!query('p.error').length) { var p = document.createElement('p'); p.className = 'error'; p.innerHTML = 'Incorrect password.'; form.insertBefore(p, form.firstChild); } }); }

• Nice animation library, but a better way of chaining animations would be useful

• Severe namespacing (YAHOO was picked because it was so ugly no one would ever have used it for an existing variable)

• Not too many shortcuts outside of dealing with browser difficulties

• Excellent documentation

Download API Docs Tips and Tutorials Blog Discuss Contribute

Prototype is a JavaScript Framework that aims toease development of dynamic web applications.

Featuring a unique, easy-to-use toolkit for class-driven

development and the nicest Ajax library around, Prototype

is quickly becoming the codebase of choice for web

application developers everywhere.

Prototype and script.aculo.us: The "Bungee

book" has landed!

Core team member Christophe

Porteneuve has been hard at work

for the past few months tracking

and documenting Prototype for his

new book Prototype and

script.aculo.us, which is now

available as a Beta Book from the

Pragmatic Programmers (and is

scheduled to ship later this year).

Read more !

DownloadGet the latest version—1.5.1

LearnOnline documentation and resources.

DiscussMailing list and IRC

ContributeSubmit patches and report bugs.

Who's using Prototype?

Meet the developers

Prototype and Script.aculo.us

onSuccess: function(response) { var json = response.responseJSON; if (json.ok) { window.location = json.redirect; } else { form.shake(); // No apparent way of setting an // "on finished" callback setTimeout(function() { if (!$$('p.error').length) { var p = new Element( 'p', {'class': 'error'} ).insert('Incorrect...'); form.insertBefore(p, form.firstChild); } }, 500); $('password').value = ''; $('password').focus(); }}

• Adds many functions to the global namespace ($, $$ etc) and extensively modifies built in types

• Heavily inspired by Ruby and Ruby on Rails

• Useful shortcuts and nice effects

• Documentation still leaves something to be desired - API docs for Prototype, incomplete wiki docs for Scriptaculous

The Dojo Toolkit

dojo.require('dojox.fx');djConfig.usePlainJson = true;

dojo.addOnLoad(function() { dojo.byId('username').focus(); dojo.query('form').connect('submit', function(ev) { dojo.stopEvent(ev); var form = this; var url = form.action; dojo.xhrPost({ handleAs: 'json', headers: {'X-Requested-With': 'XMLHttpRequest'}, url: url, form: form, load: function(json) { ... } }); });});

load: function(json) { if (json.ok) { window.location = json.redirect; } else { form.style.position = 'relative'; var last = dojo.animateProperty({ node: form, duration: 100, properties: {left: {end: 0}} }); var leftArgs = { node: form, duration: 100, properties: {left: {end: -10}} }; var rightArgs = { node: form, duration: 100, properties: {left: {end: 10}} }; dojo.fx.chain([ dojo.animateProperty(leftArgs), dojo.animateProperty(rightArgs), dojo.animateProperty(leftArgs), dojo.animateProperty(rightArgs), last ]).play();

dojo.connect(last, 'onEnd', function() { if (!dojo.query('p.error').length) { var p = document.createElement('p'); p.className = 'error'; p.innerHTML = 'Incorrect username or password.'; form.insertBefore(p, form.firstChild); } }); dojo.byId('password').value = ''; dojo.byId('password').focus();

• core, dijit and dojox:

• Small, powerful abstraction library

• Widget creation tools plus many widgets

• “The future today” genius extensions

• Documentation has improved with the Dojo Book, but still patchy in places

mooTools

• Started as an effects library for Prototype, now its own thing but Prototype influences are clear

• No intention at all of playing nicely with other libraries

• Good API documentation (including a mootorial) but not much else, and major changes between library versions

• I found the API unintuitive compared to the others

jQuery

jQuery(function($) { $('#username').focus(); $('form').submit(function() { var $this = $(this); var url = $this.attr('action'); var data = $this.serialize(); jQuery.post(url, data, function(json) { if (json.ok) { window.location = json.redirect; } else { $('#password').val('').focus(); $this.shake(function() { if (!$this.find('p.error').length) { $this.prepend('<p class="error">Incorrect ...</p>'); } }); } }, 'json'); return false; });});

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 );};

• Powerful, concise API based around CSS selector querying and chaining

• Excellent namespace management - everything lives on the one jQuery symbol which is aliased to $, with the option to revert

• Excellent support for plugins

• The best documentation out of all of the libraries

Unobtrusive scripting with jQuery

Why jQuery

• It has the best balance between simplicity, productivity and good manners

• It has excellent documentation

• You can learn the whole library in less than an hour

Why jQuery instead of...?

• Unlike Prototype and mooTools...

• ... it doesn’t populate your global namespace

• Unlike YUI...

• ... it’s extremely succinct

• Unlike Dojo...

• ... you can learn it in 45 minutes!

Learning

jQueryin 45 minutes

jQuery philosophy

• Focus on the interaction between JavaScript and HTML

• (Almost) every operation boils down to:

• Find some stuff

• Do something to it

Sidenotes with jQuery

jQuery(function($) { $('a.sidenote').click(function() { window.open($(this).attr('href'), 'popup', 'height=500,width=400,toolbar=no'); return false; });});

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

jQuery('#nav')

jQuery('div#intro h2')

jQuery('#nav li.current a')

$('#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)

Magic selectors

div:first, h3:last

:header

:hidden, :visible

:animated

:input, :text, :password, :radio, :submit...

div:contains(Hello)

jQuery collections

• $('div.section') returns a jQuery collection

• You can 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

• You can call methods on it

$('div.section').size() = no. of matched elements

$('div.section').each(function() {

console.log(this);

jQuery collections

• You can call methods on it

$('div.section').size() = no. of matched elements

$('div.section').each(function(i) {

console.log("Item " + i + " is ", this);

HTML futzing

$('span#msg').text('The thing was updated!');

$('div#intro').html('<em>Look, HTML</em>');

Attribute futzing

$('a.nav').attr('href', 'http://flickr.com/');

$('a.nav').attr({

'href': 'http://flickr.com/',

'id': 'flickr'

$('#intro').removeAttr('id');

CSS futzing

$('#intro').addClass('highlighted');

$('#intro').removeClass('highlighted');

$('#intro').toggleClass('highlighted');

$('p').css('font-size', '20px');

$('p').css({'font-size': '20px', color: 'red'});

Grabbing values

• Some methods return results from the first matched element

var height = $('div#intro').height();

var src = $('img.photo').attr('src');

var lastP = $('p:last').html()

var hasFoo = $('p').hasClass('foo');

var email = $('input#email').val();

Traversing the DOM

• jQuery provides enhanced methods for traversing the DOM

$('div.section').parent()

$('div.section').next()

$('div.section').prev()

$('div.section').nextAll('div')

$('h1:first').parents()

Handling events

$('a:first').click(function(ev) {

$(this).css({backgroundColor: 'orange'});

return false; // Or ev.preventDefault();

Handling events

$('a:first').click(function(ev) {

$(this).css({backgroundColor: 'orange'});

return false; // Or ev.preventDefault();

$('a:first').click();

Going unobtrusive

$(document).ready(function() {

alert('The DOM is ready!');

Going unobtrusive

$(function() {

Going unobtrusive

jQuery(function($) {

Chaining

• Most jQuery methods return another jQuery object - usually one representing the same collection. This means you can chain methods together:

$('div.section').hide().addClass('gone');

Advanced chaining

• Some methods return a different collection

• You can call .end() to revert to the previous collection

Advanced chaining

• Some methods return a different collection

• You can call .end() to revert to the previous collection

$('#intro').css('color', '#cccccc').

find('a').addClass('highlighted').end().

find('em').css('color', 'red').end()

• jQuery has excellent support for Ajax

$('div#intro').load('/some/file.html');

• More advanced methods include:

$.get(url, params, callback)

$.post(url, params, callback)

$.getJSON(url, params, callback)

$.getScript(url, callback)

Animation

• jQuery has built in effects:$('h1').hide('slow');

$('h1').slideDown('fast');

$('h1').fadeOut(2000);

• You can chain them:$('h1').fadeOut(1000).slideDown()

$("#block").animate({

width: "+=60px",

opacity: 0.4,

fontSize: "3em",

borderWidth: "10px"

}, 1500);

Or roll your own...

Plugins

• jQuery is extensible through plugins, which can add new methods to the jQuery object

Jazz up your JavaScript: Unobtrusive scripting with JavaScript libraries

link link

unobtrusive javascript

javascript use javascript

javascript existing

event var link

internet explorer link

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