This document summarizes the results of performance testing and experiments on the Etsy mobile listing page. It describes testing lazy loading images, reducing CSS file size, switching to SVGs, and reducing JavaScript file size. Synthetic tests and real user monitoring showed improvements in load times, especially on mobile. Further work is still needed to fully optimize frontend performance and architecture to better match the development culture. Performance directly impacts conversion rates, so continued optimization can increase sales.

1. STARRING KATIE SYLOR-MILLER AND ETSY FRONTEND SYSTEMS

2. Staff Software Engineer
ETSY Frontend Systems
Findme @ksylor and ohshitgit.com @ohshitgit

3. Indiana Jones ™ & © 2018 Lucasfilm Ltd.

5. Indiana Jones ™ & © 2018 Lucasfilm Ltd.

6. Archaeology is the study
of human culture through
it’s physical remains

7. Performance archaeology
uncovers insights into
your development culture

8. Survey
Excavate
Hypothesis
Interpret
Archaeology 101

9. Indiana Jones ™ & © 2018 Lucasfilm Ltd.

10. The Mobile Listing Page

11. Hypothesis
Image by HeritageDaily on Wikipedia

12. Mobile Visits
67% 52%
Mobile GMS

13. RUM Dom Content Loaded Times
1000 2000 3000 4000 50000
DOMContentLoaded ms
Numberofvisits

14. Dom Content Loaded Times
15%
37%
24%
13%
6%
1000 2000 3000 4000 50000
DOMContentLoaded ms
Numberofvisits

15. Conversion Vs. Dom Content Loaded
1000 2000 3000 4000 5000
DOMContentLoaded ms
Conversionrate

16. 1000 2000 3000 4000 5000
Conversion Vs. Population
15%
37%
24%
13%
6%
DOMContentLoaded ms
Conversionrate Percentage of visits

17. Improving the performance
of the listing page will
increase conversion
Hypothesis

18. Indiana Jones ™ & © 2018 Lucasfilm Ltd.

19. Survey
Hypothesis

20. Performance Best Practices
Great server response times
Minify and gzip static JS and CSS assets
Resize and compress images
Responsive images (mostly)
Use proper headers to take advantage of browser caching
Use dns-prefetch resource hints
Use HTTP/2 when available
In-house RUM monitoring and alerting
3rd party synthetic monitoring service

21. Indiana Jones ™ & © 2018 Lucasfilm Ltd.

22. Perceived Performance
How quickly users:
• receive confirmation that the page has started loading?
• see the most important information on the page?
• can interact with the page?

23. Optimize the loading
and rendering of
above-the-fold content
Critical Rendering Path

24. Indiana Jones ™ & © 2018 Lucasfilm Ltd.

25. Ground Penetrating Radar
Image by Tapatio via Wikipedia

26. WebPageTest.org
Ground Penetrating Radar

27. The Mobile Listing Page

28. WebPageTest Results
iPhone 6 iOS9 - 3GSlow
(this is much worse than our typical user experience)
METRIC BEFORE AFTER CHANGE
TTFB 1.8s
Start Render 8.5s
DOM Content Loaded 12.1s
Speed Index 13,193
Time to First Interactive >19s
CSS size 98KB/0.62MB
JS size 386KB/1.46MB
Images 37
Cost $$$$-

29. Indiana Jones ™ & © 2018 Lucasfilm Ltd.

30. Waterfall (before)

31. Waterfall (before)
Five CSS files
Block CSSOM construction
and Start Render

32. Waterfall (before)
Related listings images
(below the fold)

33. Waterfall (before)
Two different sizes of shop avatar image
(1 above, 1 below the fold)

34. Waterfall (before)
Three JS files
Global base (XL), page-specific (L), category nav(S)
Block DOM Content Loaded

35. Waterfall (before)
Similar listing images
(waaaayyyyy below the fold)

36. Five CSS bg-images
One icon font

37. Main listing image is 36th!!!
Followed by more carousel images

38. Reviews images (from async content)
Logging
Logging
Logging

39. $(‘document’).ready()

40. Indiana Jones ™ & © 2018 Lucasfilm Ltd.

41. Areas For Improvement
• Lazyload images:
Defer loading of “below the fold” images
• Reduce CSS File Size:
Combine CSS files and remove unused rules
• Switch to SVGs:
Replace CSS bg-images and icon fonts with SVGs
• Reduce JS File Size:
Remove unused Javascript

42. Survey
Excavate

43. Test Pits

44. Lazyload
Images
Test Pit #1

45. 37 Images
814KB

47. lazy loading synthetic tests
DOMContentLoadedms
1750
3500
5250
7000
Network Speed
Wifi 4G 3G
Before
After Lazy Loading

48. Reduce CSS
File Size
Test Pit #2

49. 5 CSS files
98KB/0.62MB

50. Automation to the Rescue?
• Selenium script opens the page(s) in a browser
• Run uncss (https://github.com/uncss/uncss)
• Output a new file with only the CSS in use
… But, we didn’t capture *all* states and had to keep adding
more every time we found a bug.

51. CSS Reduction Synthetic Tests
DOMContentLoaded(ms)
1750
3500
5250
7000
Network Speed
Wifi 4G 3G
Before
After CSS Reduction
After Lazy Loading

52. Lazyloading + CSS Reduction
Experiment Results
User-facing experiment #1

53. RUM Results - Lazyloading + CSS Reduction
METRIC BEFORE AFTER CHANGE
TTFB 1.16s 1.18s 1.2%
DOM Content Loaded 3.3s 3.1s 6% ➡
Page Load 6.0s 5.2s 13.2% ➡

54. RUM Results - Lazyloading + CSS Reduction

55. Conversion

56. Indiana Jones ™ & © 2018 Lucasfilm Ltd.

57. Switch to
SVGs
Test Pit #3

58. 5 bg-images
1 icon font

59. SVG Switch Synthetic Tests
Logged Out
DOMContentLoadedms
1500
3000
4500
6000
Wifi 4G 3G
Before
After SVGs
Logged In
1500
3000
4500
6000
Wifi 4G 3G
Before
After SVGs

60. SVG Switch Results
User-facing Experiment #2

61. Indiana Jones ™ & © 2018 Lucasfilm Ltd.

62. RUM Results - SVG Switch
METRIC BEFORE AFTER CHANGE
TTFB 1.17 1.17s ⬌
DOM Content Loaded 3.0s 3.0s ⬌
Page Load 5.6s 5.5s 1%➡

63. RUM Results - SVG Switch

64. Conversion ⬌

65. WebPageTest.org again
How are we doing?

66. METRIC BEFORE AFTER CHANGE
TTFB 1.8s 2.0s 11%
Start Render 8.5s 4.8s 44% ➡
DOM Content Loaded 12.1s 12.6s ?? 4%
Speed Index 13,193 13,071 ⬌
Time to First Interactive >19s >17s 10%➡
CSS size 98KB/0.62MB 38KB/0.24MB 60%➡
JS size 386KB/1.46MB 375KB/1.59MB 3%
Images 37 25 32%➡
Cost $$$$- $$$-- $➡
WebPageTest Results
iPhone 6 iOS9 - 3GSlow

67. Waterfall - After
Down to 2 CSS Files!

68. Waterfall - After
Listing carousel images!

69. Waterfall - After
One shop avatar image!

70. Waterfall - After
Still two large JS files

71. Waterfall - After
CSS Background image
added back in by experiment

72. Logging
Reviews images (added by new experiment)
Async content

73. Stratigraphy

74. A Brief History of JS at Etsy
2010 - jQuery w/Homegrown system to
concatenate and serve JS files
2011 - Dependencies get inlined using rails-style
//=require ‘path/to/dependencies’
window.Etsy.module;
2012 - RequireJS - AMD dependencies
require([‘path/to/dependencies’],
function(dep) { });
2017 - still a mix of everything :(

76. Reduce JS
File Size
Test Pit #4

77. 56KB/264KB
121 modules
142KB/712KB
124 modules
PAGE-SPECIFIC FILE GLOBAL BASE FILE

78. Indiana Jones ™ & © 2018 Lucasfilm Ltd.
TYPES

79. Manual JS
Reduction
Test Pit #4a

80. Javascript Excavation
JS dependency
$(‘selector’)
Smarty/Mustache
templates
PHP View
PHP Controller
Experiment flags

81. Indiana Jones ™ & © 2018 Lucasfilm Ltd.

82. 56KB/264KB
42KB/177KB
25% ➡
142KB/712KB
94KB/469KB
33% ➡
PAGE-SPECIFIC FILE GLOBAL BASE FILE

83. WebPageTest Results
METRIC BEFORE AFTER CHANGE
TTFB 2.0s 1.9s 5%➡
Start Render 4.8s 4.87s 1%
DOM Content Loaded 12.6s 9.8s 22%➡
Speed Index 13,071 10,903 16%➡
Time to First Interactive >17s >15s 12%➡
CSS size 38KB/0.24MB 38KB/0.24MB ⬌
JS size 375KB/1.59MB 299KB/1.15MB 20%➡
Images 25 23 8%➡
Cost $$$-- $$$-- ⬌
iPhone 6 iOS9 - 3GSlow

84. Manual JS Reduction Results
User-facing Experiment #3

85. RUM Results - Manual JS Reduction
METRIC BEFORE AFTER CHANGE
TTFB 1.2s 1.2s ⬌
DOM Content Loaded 2.9s 2.8s 2.9%➡
Page Load 5.6s 5.5s 1.6%➡

86. RUM Results - Manual JS Reduction

87. Conversion ➡

88. Indiana Jones ™ & © 2018 Lucasfilm Ltd.

89. Javascript
Instrumentation
Test Pit #4b

90. Code Coverage?

91. window.Etsy =
window.Etsy || {};
window.Etsy.Vimes.register
(“vb383”);
function vb383(id,fn) {
return function() {
window.Etsy.Vimes.start('vb383'
, id);
return fn.apply(this,
arguments);
};
}
return vb383(1, function(args)
{
return stuff;
}
Re-write JS to log
function calls
Capture real user
actions
Send logs onLoad
and onUnLoad
Map # of calls back
to source files
Introducing Vimes

93. PAGE-SPECIFIC FILE
56KB/264KB
40KB/173KB
28% ➡
142KB/712KB
89KB/448KB
37% ➡
GLOBAL BASE FILE

94. Instrumented JS Reduction
Results
Fourth Experiment

95. RUM Results - Instrumented JS
METRIC BEFORE AFTER CHANGE
TTFB 1.2s 1.2s ⬌
DOM Content Loaded 3.0s 2.9s 2.7%➡
Page Load 5.2s 5.1s 1.2%➡

96. RUM Results - Instrumented JS

97. Conversion

99. Excavate
Interpret

100. Performance directly
affects conversion

101. Frontend performance
is just as important as
backend, if not more.

102. Indiana Jones ™ & © 2018 Lucasfilm Ltd.

103. Our experiences are not
our users experiences
(especially on mobile)

104. Small-scale
performance tweaks
don’t always pan out

105. Your architecture
needs to match your
development culture

106. Static top-level
CSS or JS
dependency
managed at the
page level
Dynamic FE
dependency
management at
the component
level
WHAT WE HAVE WHAT WE NEED

107. Architect for deletion

108. Thank you!
Indiana Jones ™ & © 2018 Lucasfilm Ltd.
@KSYLOR