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JavaScript is arguably the most important language in the world. It comes included in nearly every desktop and mobile browser. It powers the client-side of apps like Facebook and GMail. It is the language of choice for mobile development environments like Apccelerator's Titanium and Apache's Cordova (aka Adobe's PhoneGap). It is even on the server now in Node.js. Yet when programmer's run into performance issue with JavaScript their first inclination is to blame its interpreted nature, not realizing that simple changes in the structure of their code can result in sometimes significant improvements in performance. In this session I will show five quick changes you can make to your JavaScript code to improve its performance and explain why they work.
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5 Quick JavaScript Performance
Improvement Tips30 January 2014
Twitter handle: @therockncoder
The Rock n Coder
• http://therockncoder.blogspot.com
• http://www.youtube.com/user/rockncoder
• https://github.com/Rockncoder
• http://www.slideshare.net/rockncoder
Our Agenda
• Why Performance Matters
• 5 Performance Tips
• Resources
• Summary
Why Performance Matters?
Why Performance Matters?
• 47% of consumers expect a 2 second page load
• 40% abandon a page that takes 3 seconds or more to load
• A 1 second delay in page response can result in a 7% reduction in conversions
If an e-commerce site is making $100,000 a day in sales, a 1 second
page delay could potentially cost you $2.5 million in lost sales every year
We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. Yet we should not pass up
our opportunities in that critical 3%. D. Knuth
5 Performance Tips
Tip #5 Use as few files as
possible
Use as few files as possible
• Browser can load multiple files at a time
• But only one JS file at a time
• Concatenate multiple JS file into one
• Compress JS files
• Prefer JS at the bottom of the HTML file
Tip #4 Prefer local variables
Prefer local variables
• Variables in scope found quicker
• JS search local scope, then global
• with creates a new scope level ahead of local
• closures also create new scope level
Var Scoping Demo
Prefer local variables
• Property chains similar to var scoping
• Objects closer in the chain found quicker
Property Chain Demo
Tip #3 Reduce the work done
in loops
Reduce the work done in loops
• No real speed difference between: for, while and do_while
• Avoid for_in
• (Watch library based for_each)
Tip #2 Watch your plugins
Watch your plugins
• Know what your plugins do
• Be sure to evaluate different plugins
• Example jQuery.js or Zepto.js
jQuery Demo
Tip #1 Avoid the DOM
Avoid the DOM
• The DOM is REALLY Slow
• Avoid accessing it when possible
• Do work offline then update DOM
DOM Access Demo
Resources
Resources
• Microsoft Ajax Minifierhttp://ajaxmin.codeplex.com/
• Google Closure Toolshttps://developers.google.com/closure/
• Yahoo YSlow http://developer.yahoo.com/yslow/
Books
• High Performance JavaScriptNicholas C. Zakas
• JavaScript NinjaJohn Resig & Bear Bibeaults
• JavaScript: The Good PartsDouglas Crockford
Summary
Summary
• Avoid the DOM
• Watch your plugins
• Reduce the work done in loops
• Prefer local variables
• Use as few files as possible
The Rock n Coder
• http://therockncoder.blogspot.com
• http://www.youtube.com/user/rockncoder
• https://github.com/Rockncoder
• http://www.slideshare.net/rockncoder
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