Doris Chen, a developer evangelist at Microsoft with over 18 years of experience, emphasizes the importance of cross-browser testing and feature detection in web development to ensure website compatibility. The document discusses various testing tools, CSS vendor prefixes, and the significance of polyfills and fallbacks for unsupported features across different browsers. It advocates for using Modernizr for feature detection and highlights the drawbacks of relying on user agent strings for browser detection.

1. Doris Chen Ph.D.
Developer Evangelist
Microsoft
doris.chen@microsoft.com
@doristchen
Building Web Sites that
Work Everywhere

2. Who am I?
 Developer Evangelist at Microsoft based in Silicon
Valley, CA
 Blog: http://blogs.msdn.com/b/dorischen/
 Twitter @doristchen
 Email: doris.chen@microsoft.com
 Has over 18 years of experience in the software industry
focusing on web technologies
 Spoke and published widely at OSCON, Fluent, HTML5
DevConf, JavaOne, O'Reilly, Silicon Valley Code Camp,
and worldwide User Groups meetings
 Doris received her Ph.D. from the University of California
at Los Angeles (UCLA)

3. Agenda
PAGE 3
Cross Browser Testing
Browser Detection and User Agent
Polyfills and Fallbacks
Summary
Feature Detection
CSS3 and Vendor Prefixes

4. Cross Browser Testing
4

6. MICROSOFT CONFIDENTIAL
Interoperable intersection
TheMobileWeb

7. Testing Tools
 Site Scan (Free)
 Reports back on common coding problems
 https://dev.windows.com/en-us/microsoft-edge/tools/staticscan/
 Browser screenshots (Free)
 Take screenshots of your site in a selection of common browsers and devices
 https://dev.windows.com/en-us/microsoft-edge/tools/screenshots/
 Windows virtual machines (Free)
 free downloads of Windows virtual machines used to test IE6 - IE11
 Need to have a platform for hosting virtual machines: VirtualBox, VMware Fusion
and Parallels
 https://dev.windows.com/en-us/microsoft-edge/tools/vms/windows/
 BrowserStack
 A paid online service that gives you access to hundreds of virtual machines
 Quickly test sites from your browser without installing any actual virtual
machines
 Supports local tunneling, so your site doesn't have to be live
 http://www.browserstack.com/

8. Testing Tools
Demo

9. CSS3 and Vendor Prefixes
12

10. Vendor Prefixes
 Browser vendors oftentimes use vendor-specific prefixes to
implement new features before they are W3C
recommendations
 Once a feature or property is a W3C recommendation,
browsers usually will support the non-prefixed versions
 Examples of vendor prefixes:
 Vendor prefixes are still needed to support older browser
versions, even after the browser vendors have adopted the
non-prefixed versions in newer versions
13
-ms-
-moz-
-o-
-webkit-
Microsoft
Mozilla
Opera
Safari and other WebKit-based browsers

11. When to Use CSS Prefixes
Common properties & values that need prefixed:
animation
box-sizing
Flexbox layout module properties
CSS regions
transition
transform
CSS grid layout
filter
calc() unit value
16

12. When to NOT Use Prefixes
Common properties that don't need prefixed:
border-radius
box-shadow
font-face
opacity
text-shadow
pointer-events
max-height
min-height
17

13. Prefix Tools
 Autoprefixer
 Parses CSS files and adds appropriate vendor prefixes
 Allows you to write CSS without worrying about what prefixes
you should use
 Vendor prefixes are pulled from caniuse.com
 Autoprefixer is a "post-processor", meaning it runs after your
Sass, Stylus or Less has been compiled
 Use Autoprefixer with Grunt
 https://autoprefixer.github.io/
 -prefix-free
 Use only unprefixed CSS properties
 Adding the current browser’s prefix to any CSS
 http://leaverou.github.io/prefixfree/#test-drive
18

14. Prefix tools
Demo

15. Browser Detection and User Agent
22

16. Browser Fragmentation

17. Fragmentation
 Varying Levels of Support
 Across browsers
 Across browser versions
 New versions released
constantly
 Browser detection doesn’t
work
 Fixes based on assumptions
 Full-time job tracking
changes

18. Browser Detection: User Agent
 Each browser User Agent through the years tried to
mimic others
 Lead to very complicated logic when UA sniffing
 Many browsers try to act like other browsers to claim
they support each other
 In the past, the user agent string was used to change
code per browser (sometimes via a JavaScript plugin)
 No longer a recommended technique
 Much better technique is to use feature detection
26

19. User-Agent Strings
Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko)
Chrome/39.0.2171.71 Safari/537.36 Edge/12.0
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_1) AppleWebKit/600.1.25 (KHTML, like Gecko)
Version/8.0 Safari/600.1.25
Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko)
Chrome/40.0.2214.93 Safari/537.36
Mozilla/5.0 (Windows NT 10.0; WOW64; rv:35.0) Gecko/20100101 Firefox/35.0

20. User Agent Sniffing
 Very inexact and can easily be spoofed
 You can end up with very messy browser testing logic:
if (ie) {
if (ie.version === 7) { ... }
} else if (firefox) {
...
} else { ... } // and on and on
 Much less maintainable as browsers evolve
31

21. Feature Detection

22. Feature Detection
 Based on what browsers support, not their versions
 Check for the feature you want to use
 Object, Method, Property, Behavior
 Detect for standards-based features
first
 Browsers often support both standards and
legacy
 Standards are your most stable ground to build
upon
 Dynamically load custom code to mimic missing
features

23. Why not Check for a
Browser?
// If not IE then use addEventListener…
if (navigator.userAgent.indexOf("MSIE") == -1) {
window.addEventListener( “load”, popMessage, false );
} else if (window.attachEvent) {
window.attachEvent( “onload”, popMessage);
}
Bad

24. Why not Check for a
Browser?
if (window.addEventListener) {
window.addEventListener( “load”, popMessage,
false );
} else if (window.attachEvent) {
window.attachEvent( “onload”, popMessage);
}
Good

25. Feature Detection
 Best option in my opinion for this…
 http://www.modernizr.com/

26.  Best feature detection Support
 Detects:
 All major HTML5 features
 All major CSS3 features
 Constantly updated
 Can create a bundle of the tests needed
 Utilize one of the many Modernizr test scripts
 Create a custom script
 Also has polyfills to keep older browsers
supported

27. Get Custom Build

28. function(){
var
sheet, bool,
head = docHead || docElement,
style = document.createElement("style"),
impl = document.implementation || { hasFeature: function() { return false; } };
style.type = 'text/css';
head.insertBefore(style, head.firstChild);
sheet = style.sheet || style.styleSheet;
var supportAtRule = impl.hasFeature('CSS2', '') ?
function(rule) {
if (!(sheet && rule)) return false;
var result = false;
try {
sheet.insertRule(rule, 0);
result = (/src/i).test(sheet.cssRules[0].cssText);
sheet.deleteRule(sheet.cssRules.length - 1);
} catch(e) { }
return result;
} :
function(rule) {
if (!(sheet && rule)) return false;
sheet.cssText = rule;
return sheet.cssText.length !== 0 && (/src/i).test(sheet.cssText) &&
sheet.cssText
.replace(/r+|n+/g, '')
.indexOf(rule.split(' ')[0]) === 0;
};
bool = supportAtRule('@font-face { font-family: "font"; src: url(data:,); }');
head.removeChild(style);
return bool;
};
Test for @font-face
You can do this

29. Test for @font-face
Or ….
if (Modernizr.fontface){
…
}

30. Demo

31. Polyfills and Fallbacks

32. Polyfills
 What are they?
 Typically JavaScript, HTML & CSS code
 What do they do?
 Provides support for missing features
 When do you use them?
 Use them to fallback gracefully or mimic
functionality
 Modernizr will polyfill HTML5 elements automatically
 Help load polyfills for nearly every feature it detects
 Create your own polyfill, or use existing ones

33. Example Manual Polyfill
if (!window.localStorage) {
window.localStorage = {
getItem: function (key) { /* ... */ },
setItem: function (key, val) { /* ... */ },
clear: function () { /* ... */ }
/* ... */
};
}
53

34. Example Polyfill with Modernizr
Modernizr.load({
test: Modernizr.geolocation,
yep: 'geo.js',
nope: 'geo-polyfill.js'
});
54

35. Polyfills: Examples
Video Tags

36. HTML5 Video & Audio
<audio <video
src= src= The url to the audio or video
width= The width of the video element
height= The height of the video element
poster= The url to the thumbnail of the video
preload= preload= (none, metadata, auto) Start downloading
autoplay autoplay Audio or video should play immediately
loop loop Audio or video should return to start and play
controls controls Will show controls (play, pause, scrub bar)
> >
… …
</audio> </video>

37. Compatibility Table
HTML5 Audio
MP3
audio
support
Yes
Yes Yes Yes Yes Yes
WAV PCM
audio
support
Yes
No Yes Yes Yes Yes
AAC audio
format
Yes
Yes Yes(*) Yes Yes Yes

38. Compatibility Table
HTML5 <video>
VP8
(WebM)
video
support
Yes (*)
Yes
Yes No (*) Yes Yes
H.264
video
format
(MPEG-4)
Yes
Yes Yes Yes Yes
Ogg/
Theora
Consider No Yes No Yes Yes

39. Elements With Fall Backs
PAGE 60
Browsers won’t render elements
they don’t understand...
But, they will render what’s
between those elements
For example:
<video src=“video.mp4”>
What will it render?
</video>

40. HTML5 <video> : Degrading Gracefully
<video src="video.mp4" poster="movie.jpg"
height="480" width="640"
autoplay autobuffer controls loop>
<!-- Flash/Silverlight video here -->
<script type="text/javascript">
var so = new SWFObject(“video.swf”);
so.addParam("allowFullScreen","true");
so.addVariable("autostart","true");
…
</script>
</video>
 Multiple video sources to support multiple browsers

41. Plugin Free Experience:
http://www.worldstarhiphop.com/vi
deos/video.php?v=wshhNPy952Q9
wUk3n353
Demo

42. Take Away
 Avoid browser detection, User Agent Sniffing
 Browsers change
 Varying levels of feature support across all major
browsers
 Use feature detection
 Check for the feature you want to use
 Detect for standards first
 Use Modernizr – http://modernizr.com
 Cleaner code & they’ve done the work for you
 Polyfills and Fallbacks
 mimics a standard API to avoid a rewrite