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.

1. 5 Quick JavaScript
Performance
Improvement Tips
30 January 2014

2. Twitter handle:
@therockncoder

3. The Rock n Coder
• http://therockncoder.blogspot.com
• http://www.youtube.com/user/rockncoder
• https://github.com/Rockncoder
• http://www.slideshare.net/rockncoder

4. Our Agenda
• Why Performance Matters
• 5 Performance Tips
• Resources
• Summary

5. Why Performance
Matters?

6. 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

7. 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

8. 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

9. 5 Performance Tips

10. Tip #5
Use as few files as
possible

11. 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

12. Tip #4
Prefer local variables

13. 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

14. Var Scoping Demo

15. Prefer local variables
• Property chains similar to var scoping
• Objects closer in the chain found quicker

16. Property Chain Demo

17. Tip #3
Reduce the work done
in loops

18. Reduce the work done
in loops
• No real speed difference between: for, while
and do_while
• Avoid for_in
• (Watch library based for_each)

19. Tip #2
Watch your plugins

20. Watch your plugins
• Know what your plugins do
• Be sure to evaluate different plugins
• Example jQuery.js or Zepto.js

21. jQuery Demo

22. Tip #1
Avoid the DOM

23. Avoid the DOM
• The DOM is REALLY Slow
• Avoid accessing it when possible
• Do work offline then update DOM

24. DOM Access Demo

25. Resources

26. Resources
• Microsoft Ajax Minifier
http://ajaxmin.codeplex.com/
• Google Closure Tools
https://developers.google.com/closure/
• Yahoo YSlow
http://developer.yahoo.com/yslow/

27. Books
• High Performance JavaScript
Nicholas C. Zakas
• JavaScript Ninja
John Resig & Bear Bibeaults
• JavaScript: The Good Parts
Douglas Crockford

28. Summary

29. Summary
• Avoid the DOM
• Watch your plugins
• Reduce the work done in loops
• Prefer local variables
• Use as few files as possible

30. The Rock n Coder
• http://therockncoder.blogspot.com
• http://www.youtube.com/user/rockncoder
• https://github.com/Rockncoder
• http://www.slideshare.net/rockncoder