Download - Progressive Enhancement With JavaScript

Aaron Gustafson

AN EVENT APART - 25 APRIL 2008

Progressive Enhancement with JavaScript

PROGRESSIVE ENHANCEMENT WITH JAVASCRIPT


What isProgressive

Enhancement?

2



ProgressiveEnhancement

vs.Graceful

Degradation

3



Graceful Degradation! A holdover from engineering

! Build for the latest browsers

! Test on older devices

! Happens at the end

! Accounts for few versions

! Expects a poor experience for older browsers

! Fixes major issues but little else

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AN EVENT APART - 25 APRIL 2008 5



Progressive Enhancementfocuses on contentcontent

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Content is why we build websites

and should beour central focus

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How does it work?

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Flavorful nugget of content(semantic goodness)



Rich, indulgent design



Sweet interactivity(keeps it from melting in your hands)



Technologies applied as layers

14



(Mr. Clarke’s web standards trifle)



Why a peanut m&m?



The peanut is good for

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! diabetics

! search engine spiders

! mobile devices



It’s a basic levelof support



! some browsers only handle a certain level of CSS

! some companies turn o" JavaScript

Rich, chocolaty goodness



It can be beautiful(and progressive)



The candy coating

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! JavaScript can turn a website into an experience

! we can deliver our scripts a la carte



How do we do it?



Restraint& Planning

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Wieldyour power

wisely

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Dear George Lucas, please don’t sue me. Kthxbye.

A long time ago, in acubicle far, far away...

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DHTML

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(was awful)



Spaghetti code

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(our HTML was spaghetti too)



Things are better now,but we have new challenges

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What canJavaScript do?

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How shouldJavaScriptbe used?

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JavaScript



Progressive Enhancementhelps us by reminding usto focus on the content

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Back to basics

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XHTML + HTTP



Back to basics

33

solid foundation



All code neededto understandand use a site

should exist beforeany scripts run

PE Maxim:

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Period.

PE Maxim:

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Consider lala.com

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Without JavaScript

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Without JavaScript

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Doh!



And looking at the markup...

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And looking at the markup...

37

Ugh!



What about search?

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What aboutalternative devices?

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EnterUnobtrusiveJavaScript

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the cornerstone of ProgressiveEnhancement with JavaScript( )



Don’t do this

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<a href="javascript:someFunction();">some text</a>

or

<a href="javascript:void(null);" onclick="someFunction();">some text</a>

or

<a href="#" onclick="someFunction();">some text</a>



An improvement, but still...

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<a href="http://offsite.com" onclick="newWin( this.href ); return false;"> some text</a>

http://offsite.com

http://offsite.com



document.getElementsByTagName( 'body' )[0].onclick = clickDelegator;

function clickDelegator( e ){ e = ( e ) ? e : event; var el = e.target || e.srcElement;

// external links

if( el.nodeName.toLowerCase() == 'a' && el.getAttribute( 'rel' ) == 'external' ){ newWin( el.href ); }}

You’re hot

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Keep the hot side hotand the cold side cold

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or getting some separationbetween your CSS and JS( )



Remember stu" like this?

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<a href="foo.html" style="color:blue;" onmouseover="this.style.color='red'"

onmouseout="this.style.color='blue'">Foo</a>



Remember stu" like this?

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<a href="foo.html" style="color:blue;" onmouseover="this.style.color='red'"

onmouseout="this.style.color='blue'">Foo</a>

Obvisouly, we should be doing this instead:

a, a:link, a:visited { color: blue;}

a:hover { color: red;}



CSS waspoorly understood

back then

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but we knowbetter now



don’t we?



Hmm...

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for( i=0; i<objects.length; i++){ objects[i].style.display = 'none';}



Better

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for( i=0; i<objects.length; i++){ objects[i].style.position = 'absolute'; objects[i].style.left = '-999em';

}



Separation

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CSS:

.hidden { position: absolute; left: -999em;}

JavaScript:

for( i=0; i<objects.length; i++){ objects[i].addClassName( 'hidden' );

}



Maintenance options

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! external style rules added to master CSS file by hand

! external CSS file added to the document by hand

! external CSS file added to the document via script

! embedding CSS in the document via script



But keep in mind

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you need toavoid applying

script-related styles



until you knowyour script can run

and it hasinitialized properly



How do we do that?

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! make your style rules specific:

.TabInterface-folder {

...

}

or

#TabInterface .tab {

...

}

#TabInterface .tab.active {

...

}



How do we do that?

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! turn “on” script-related rules at run-time:

<div id="main" class="tabbed">

becomes

<div id="main" class="tabbed-on">



How do we do that?

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! turn “on” script-related rules at run-time:

Default Activated

add “-on” to the class .tabbed .tabbed-on

add an activation class .auto-submit .auto-submit.active

change the form of the class .replace-me .replaced



Become a detective

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Look for methods

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function someFunction(){ if( !document.getElementsByTagName ) return; // code that uses document.getElementsByTagName()

...}



Look for methods

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function someFunction(){ if( !document.getElementsByTagName || !document.getElementById ) return;

/* code that uses document.getElementsByTagName() and document.getElementById() */}



Look for elements

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function someFunction(){ if( !document.getElementsByTagName || !document.getElementsByTagName( 'p' ) ) return;

/* code that uses document.getElementsByTagName() and requires the presence of a P element */ ...}



Look for identified elements

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function someFunction(){ if( !document.getElementById || !document.getElementById( 'content' ) ) return;

// code that requires the presence of #content ...}



Look for objects

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function someFunction(){ if( typeof( Prototype ) == 'undefined' ) return; // code that uses Prototype

...}



Look for object versions

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function someFunction(){ if( typeof( Prototype ) == 'undefined' || parseFloat( Prototype.Version ) < 1.5 ) return;

// code that uses Prototype 1.5 or higher ...}



Look before you leap

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window.onload = function(){ if( document.getElementsByTagName && document.getElementById ){

someFunction(); }};



Be progressive

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! Start with the content, then work your way out

! Get unobtrusive

! Keep some distance between your styles & your scripts

! Put on your detective hat



Questions?