Slide 1
Slide 1 text
Speed Index,
Explained!
Stefan Baumgartner | @ddprrt https://speakerdeck.com/ddprrt/speed-index-explained
Slide 2
Slide 2 text
The page has to load in under
3 seconds
Slide 3
Slide 3 text
No content
Slide 4
Slide 4 text
It works on my machine!
Slide 5
Slide 5 text
No content
Slide 6
Slide 6 text
The Dothraki have no word
for “works on my machine”
Slide 7
Slide 7 text
Use metrics!
Slide 8
Slide 8 text
loading
document.readyState
loading
DOMContentLoaded
window.onload
Slide 9
Slide 9 text
window.performance.timing
Slide 10
Slide 10 text
No content
Slide 11
Slide 11 text
Speed Index
Slide 12
Slide 12 text
∫ 1 - visuallycomplete/100
0
end
Slide 13
Slide 13 text
What does this mean?
Slide 14
Slide 14 text
No content
Slide 15
Slide 15 text
No content
Slide 16
Slide 16 text
No content
Slide 17
Slide 17 text
No content
Slide 18
Slide 18 text
No content
Slide 19
Slide 19 text
Visually complete (%)
0
25
50
75
100
Time in Seconds
0s 1s 2s 3s 4s 5s 6s 7s 8s
Slide 20
Slide 20 text
Visually complete (%)
0
25
50
75
100
Time in Seconds
0s 1s 2s 3s 4s 5s 6s 7s 8s
Slide 21
Slide 21 text
Visually complete (%)
0
25
50
75
100
Time in Seconds
0s 1s 2s 3s 4s 5s 6s 7s 8s
Slide 22
Slide 22 text
Visually complete (%)
0
25
50
75
100
Time in Seconds
0s 1s 2s 3s 4s 5s 6s 7s 8s
Slide 23
Slide 23 text
Visually complete (%)
0
25
50
75
100
Time in Seconds
0s 1s 2s 3s 4s 5s 6s 7s 8s
Slide 24
Slide 24 text
Visually complete (%)
0
25
50
75
100
Time in Seconds
0s 1s 2s 3s 4s 5s 6s 7s 8s
Slide 25
Slide 25 text
So, how’s difference
calculated?
Slide 26
Slide 26 text
-
=
Slide 27
Slide 27 text
6% difference
Slide 28
Slide 28 text
5% difference
Slide 29
Slide 29 text
this is not good
for the user
this is
Slide 30
Slide 30 text
No content
Slide 31
Slide 31 text
No content
Slide 32
Slide 32 text
Baseline JPEG
10%
Slide 33
Slide 33 text
Baseline JPEG
10% 50%
Slide 34
Slide 34 text
Baseline JPEG
10% 50% 100%
Slide 35
Slide 35 text
Gotcha!
Slide 36
Slide 36 text
Baseline JPEG
If the image loads gradually over 1 second,
it has a SpeedIndex of 500
Slide 37
Slide 37 text
Progressive JPEG
10% 50% 100%
Slide 38
Slide 38 text
Progressive JPEG
The image is already ~77% complete at the
beginning (it’s 23% different)
Slide 39
Slide 39 text
Progressive JPEG
So if it loads gradually over 1 second,
it has a SpeedIndex of 113
Slide 40
Slide 40 text
Some tricks …
Slide 41
Slide 41 text
Webfonts
Slide 42
Slide 42 text
Modern
browser?
Supports
WOFF?
Font in
Storage
Show
Font
Pre-Render
Slide 43
Slide 43 text
Modern
browser?
Supports
WOFF?
Font in
Storage
Show
Font
No Font
http://crocodillon.com/blog/non-blocking-web-fonts-using-localstorage
Pre-Render
Slide 44
Slide 44 text
localStorage
available?
Download
Font
Save in
localStorage
Show
Font
No Font
http://crocodillon.com/blog/non-blocking-web-fonts-using-localstorage
Post-Render
Slide 45
Slide 45 text
Critical Path CSS
Slide 46
Slide 46 text
No content
Slide 47
Slide 47 text
blocking!
Slide 48
Slide 48 text
blocking!
blocking!
Slide 49
Slide 49 text
blocking!
blocking!
start render
Slide 50
Slide 50 text
blocking!
blocking!
start render?
Slide 51
Slide 51 text
…
…
loadCSS(‘main.css’)
Slide 52
Slide 52 text
…
…
loadCSS(‘main.css’)
Slide 53
Slide 53 text
…
…
loadCSS(‘main.css’)
Slide 54
Slide 54 text
No content
Slide 55
Slide 55 text
No content
Slide 56
Slide 56 text
I’m not 100% happy with Critical Path CSS
Slide 57
Slide 57 text
No content
Slide 58
Slide 58 text
No content
Slide 59
Slide 59 text
No content
Slide 60
Slide 60 text
There is still one thing however…
Slide 61
Slide 61 text
Speed Index should give you an
idea how the user feels when
using your website
Slide 62
Slide 62 text
… so why is everything
done by a machine
Slide 63
Slide 63 text
… so why is everything
done by a machine
Slide 64
Slide 64 text
No content
Slide 65
Slide 65 text
No content
Slide 66
Slide 66 text
No content
Slide 67
Slide 67 text
No content
Slide 68
Slide 68 text
No content
Slide 69
Slide 69 text
Let’s do it on the client!
Slide 70
Slide 70 text
GetRects();
GetRectTimings();
GetFirstPaint();
GetFontTime();
CalculateVisualProgress();
CalculateSpeedIndex();
Slide 71
Slide 71 text
GetRects();
GetRectTimings();
Get the visible rectangle for the things
we care about.
Get the timings of the resources inside
Slide 72
Slide 72 text
window.performance.timing
Slide 73
Slide 73 text
window.performance.timing
getEntriesByType(‘resource’)
Slide 74
Slide 74 text
No content
Slide 75
Slide 75 text
No content
Slide 76
Slide 76 text
No content
Slide 77
Slide 77 text
GetFirstPaint();
Calculate the timing when the browser
painted first.
Slide 78
Slide 78 text
// IE and Edge
window.performance.timing.msFirstPaint
// Chropera
var times = window.chrome.loadTimes();
times.firstPaintTime
Slide 79
Slide 79 text
// Every other browser
var headURLs = {};
var headElements =
doc.getElementsByTagName('head')[0].children;
for (var i = 0; i < headElements.length; i++) {
//get stylesheets and non-async scripts
...
}
// compare with resource timing
var requests =
win.performance.getEntriesByType("resource");
Slide 80
Slide 80 text
GetFontTime();
Check all font resources and do
resource timings …
Slide 81
Slide 81 text
CalculateSpeedIndex();
Given the visual progress information,
calculate the speed index.
Slide 82
Slide 82 text
resource1
firstPaint
resource3
resource4
endofPaint
responseStart
document
font
Slide 83
Slide 83 text
resource1
firstPaint
resource3
resource4
endofPaint
responseStart
blank, 1 point per ms! gradually
document
font
Slide 84
Slide 84 text
var now = ruxitApi.now();
var actionId =
ruxitApi.enterAction(
'Speed Index',
'speedIndex',
now - RUMSpeedIndex(),
null);
ruxitApi.leaveAction(actionId, now);
Tell your monitor solution
Slide 85
Slide 85 text
https://github.com/ddprrt/RUM-SpeedIndex
Slide 86
Slide 86 text
@ddprrt
@dynatrace
@ruxit