Developing High Performance Web Apps

PERFOMANCE MATTERS
DEVELOPING HIGH
PERFORMANCE WEB
APPS
Timothy Fisher
Compuware
September 15, 2010

WHO AM I?

Timothy Fisher
Technical Consultant (Eagle)
Compuware

@tfisher
tim.fisher@compuware.com
www.timothyfisher.com

AGENDA

• Why Front-end Performance Matters
• Optimize Page Load
• Responsive Interfaces
• Loading and Executing JavaScript

AGENDA
• DOM Scripting
• Tools

• Gomez and Front-End Performance
• Questions

An overview to spark thought and further investigation

Why Front-end
Performance matters

According to Yahoo:
“80% of end-user response time is
spent on the front-end”

According to Steve Souders (Google performance guru):
“80-90% of end-user response
time is spent on the front-end”

Ads
CDN’s

Services
Syndicated Content

Integration is happening on the client-side

PAGE LOAD TIME
IS IMPORTANT
Page load time is critical to the success of a web site/app
Google: +500 ms → -20% traffic

Yahoo: +400 ms → -5-9% full-page traffic

Amazon: +100 ms → -1% sales

Small performance flucutations affect traffic and sales!!!

BEST PRACTICES

• Minimize HTTP Requests
• combine javascript and css into less number of ﬁles

• consider sprites for combining images

• Use a Content Delivery Network (CDN)
• static content delivered by fast distributed network with low latency

BEST PRACTICES

• Make Pages Cacheable
• use appropriate header tags

• Use GZIP Page Compression
• all modern browsers support GZIP compression

BEST PRACTICES

• Place Stylesheets at the Top
• browser needs style info first to avoid repaints/reflows later

• Place Scripts at the Bottom
• allow page content to be rendered first

BEST PRACTICES

• Minify JavaScript and CSS
• save bandwidth / download time

• lots of tools to automate this for you

• Post/pre Load Components
• consider how you are loading content and scripts

BEST PRACTICES

• Split Components Across Domains
• enables browser to load more stuff in parallel

• Optimize Images
• avoid high-res images unless it is intentional

• don’t let the browser scale your images

SINGLE THREAD
IMPLICATIONS

• Single UI Thread for both UI updates and JavaScript execution

• only one of these can happen at a time!

Page downloading and rendering
must stop and wait for scripts to be
downloaded and executed

“0.1 second is about the limit for having the user feel
that a system is reacting instantaneoulsy”
- Jakob Nielsen, Usability Expert

Translation: No single JavaScript should execute for
more than 100 mS to ensure a responsive UI.

LOADING & EXECUTING
JAVASCRIPT

WHY JAVASCRIPT?

• Poorly written JavaScript is the most common reason
for slow client-side performance

• Loading

• Parsing

• Execution

TYPICAL JAVASCRIPT
PLACEMENT
<html>
<head>
<link href=”style.css” rel=”stylesheet” type=”text/css”/>

<script src=”myscript.js” type=”text/javascript”></script>

<script>
function hello_world() {
alert(‘hello world’);
}
var complex_data = // some complex calculation //
</script>
</head>

<body>
...
</body>
</html>

BETTER JAVASCRIPT
PLACEMENT
<html>
<head>
<link href=”style.css” rel=”stylesheet” type=”text/css”/>
</head>

<body>
...

<script>
function hello_world() {
alert(‘hello world’);
}
var complex_data = // some complex calculation
</script>
</body>
</html>

COMBINE JAVASCRIPT FILES
• Each script request requires HTTP performance overhead

• Minimize overhead by combining scripts

file.js
file1.js file2.js file3.js

=>

Browser Browser

MINIFY JAVASCRIPT

• Removes all unecessary space/comments from your JS ﬁles

• Replace variables with short names

• Easy to do at built-time with a tool

• Checkout YUI Compressor, Closure Compiler...

Avoid manual code-size optimization!

NON-BLOCKING LOADS

• AddJavaScript to a page in a way that does not block the
browser thread

‣ Dynamic Script Elements
‣ Script Injection

DYNAMIC SCRIPT ELEMENTS

• JavaScript
is downloaded and executed without blocking
other page processes.

var script = document.createElement(‘script’);
script.type = “text/javascript”;
script.src = “file1.js”;
document.getElementsByTagName(“head”)[0].appendChild(script);

SCRIPT INJECTION
• Use Ajax to get script
• Can control when script is parsed/executed
• JavaScript must be served from same domain
var xhr = XMLHttpRequest();
xhr.open(“get”, “file.js”, true);
xhr.onreadystatechange = function() {
if (xhr.readyState == 4) {
if (xhr.status >= 200 && xhr.status < 300 || xhr.status == 304) {
var script = document.createElement(“script”);
script.type = “text/javascript”;
script.text = xhr.responseText;
document.body.appendChild(script);
}
}
};
xhr.send(null);

RECOMMENDED
NONBLOCKING LOAD

• Includethe code necessary to dynamically the the rest of the
JS required for page init

<script type="text/javascript" src="loader.js"></script>
<script type="text/javascript">
loadScript("the-rest.js", function(){
Application.init();
});
</script>

Optionally include the loadScript function directly in the page

REAL WORLD USE

• This
technique is used by many JavaScript libraries including
YUI and Dojo.

<script type="text/javascript"
src="http://yui.yahooapis.com/combo?3.0.0/build/yui/yui-min.js"></script>

YUI().use("dom", function(Y){
Y.DOM.addClass(document.body, "loaded");
});

Dynamically loads the DOM utility and calls ‘loaded’ function
when loading is complete.

SUMMARY

• Browser UI and JS share a single thread

• Code execution blocks other browser processes such as UI
painting

• Put script tags at the bottom of page

• Load as much JS dynamically as possible

• Minimize and compress your JS

DOCUMENT OBJECT MODEL

• Document Object Model (DOM) is a language
independent API for working with HTML and XML

• DOM Scripting is expensive and a common cause of
performance problems

DOM/JS ISOLATION

• DOM and JavaScript implementations are independent
of each other in all major browsers

• This causes overhead performance costs as these two
pieces of code must interface

JavaScri
DOM
pt

Minimize how many times you cross this bridge

BAD DOM SCRIPTING

Bad (we cross the bridge 1500 times!)
function innerHTMLLoop() {
for (var count = 0; count < 1500; count++) {
document.getElementById('here').innerHTML += 'a';
}
}

Good (we cross the bridge 1 time)
function innerHTMLLoop2() {
var content = '';
for (var count = 0; count < 1500; count++) {
content += 'a';
}
document.getElementById('here').innerHTML += content;
}

REPAINTS AND REFLOWS
A reﬂow occurs whenever you change the
geometry of an element that is displayed on the
page.

A repaint occurs whenever you change the
content of an element that is displayed on the
screen.

These are both expensive operations in terms of performance!

AVOIDING REPAINTS/REFLOWS
This will potentially cause 3 repaints/reﬂows...
var el = document.getElementById('mydiv');
el.style.borderLeft = '1px';
el.style.borderRight = '2px';
el.style.padding = '5px';

Better... 1 repaint/reﬂow
el.style.cssText = 'border-left: 1px; border-right: 2px; padding: 5px;';

or...
el.className = 'active';

TOOLS ARE YOUR FRIEND
The right tools can help a developer identify and ﬁx
performance problems related to client-side behaviour.

Proﬁling
Timing functions and operations during script
execution

Network Analysis
Examine loading of images, stylesheets, and scripts
and their effect on page load and rendering

FIREBUG
•Firefox plugin
•Debug JavaScript
•View page load waterfall:

PAGE SPEED
•Extension to Firebug from Google
•Provides tips for improving page performance

Y-SLOW

•Extension to Firebug from Yahoo
•tips for improving page performance

DYNATRACE AJAX EDITION

•extension for IE, coming soon for Firefox
•deeper client-side tracing than the ﬁrebug extensions

SPEED TRACER

•performance extension for Google Chrome
•similar features to Dynatrace Ajax

YUI PROFILER
•proﬁle JavaScript performance
•developer must insert JS code

MORE TOOLS...

Internet Explorer Developer Tools

Safari Web Inspector

Chrome Developer Tools

Lots of developer tools to debug performance!

GOMEZ AND FRONT-END
PERFORMANCE

GOMEZ

Gomez is the web performance division of Compuware

•Active Monitoring
synthetic tests using a dedicated node and a Gomez
controlled browser

•Actual Monitoring
tests the actual end-user experience by transmitting
data while users are browsing to a Gomez server

GOMEZ ACTIVE

• Synthetic tests
• Uses nodes in Gomez network to perform web
application testing.

• Today pure client-side metrics are not collected

GOMEZ ACTUAL

• Real User Monitoring (RUM)
• JavaScript ‘tags’ inserted into web pages.
• Tags report performance metrics to Gomez server
• Page and object load performance metrics

EXTENDING ACTIVE/ACTUAL
•Desire to collect more client-side metrics
•JavaScript - load, parse, execution timing
•CSS - load, parse timing
•full Waterfall page load metrics
•Attribute client-side performance to speciﬁc sources
(i.e. javascript library from vendor abc is the source of your slow performance)

•Expose full end-to-end performance

RESOURCES
• Yahoo Exceptional Performance
http://developer.yahoo.com/performance/

• Google Web Performance
http://code.google.com/speed

• JavaScript: The Good Parts by Douglas Crockford

• High Performance JavaScript by Nicholas Zakas

• Even Faster Websites by Steve Souders

• Steve Souders Site
http://www.stevesouders.com

• John Resig’s Blog
http://www.ejohn.org

Developing High Performance Web Apps

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