This document provides an overview of JavaScript analysis for SEO purposes. It discusses how JavaScript can impact a site's position in search engine results pages and performance. It provides tips for analyzing JavaScript-rendered content and ensuring it is properly indexed by search engines. The document also covers how to optimize JavaScript files for faster loading, including minification, compression, efficient loading, and validating third-party scripts. Checklists are provided for assessing a site's JavaScript usage and opportunities for improvement.

1. JavaScript analysis is
extremely important and
anyone can do it
July 2020
@Gaca-Tworek

2. I am Barbara Gaca-Tworek
Technical SEO Lead
Find me at @Gaca-Tworek
Hello!
2

3. JavaScript impact on SEOs
lives1,2,3,4
Position in
SERP
Indexation Performance
3
@Gaca-Tworek

4. JavaScript indexation
Basic overview and how to spot issues
1
4
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5. 5
How is this decision
being made?1
Source:
https://developers.google.com/search/docs/guides/javascript-
seo-basics
@Gaca-Tworek

6. “
Pretty much every website when
we see them for the first time
goes to rendering, so there's no
indexing before it hasn't been
rendered.
(Martin Splitt, 23.08.2019)5
6
@Gaca-Tworek

7. Google will compare server’s initial
response with the rendered page.5,6
7
Initial response Rendered page

8. How to spot JS dependent
content?
Chrome Dev Tools Disable JavaScript External tools
8
@Gaca-Tworek

9. How to look for JS dependent
content in Chrome Dev Tools?
9
@Gaca-Tworek

10. JavaScript checklist part 17
Look for
the content
rendered
by JS
Check if
this
content is
indexed.
Make sure
Google can
render it.
10
GSC
Mobile-
Friendly
Test@Gaca-Tworek

11. Web Rendering Service
What do we need to know about WRS?
2
11
@Gaca-Tworek

12. “
Googlebot and its Web Rendering
Service (WRS) component
continuously analyze and identify
resources that don’t contribute to
essential page content and may
not fetch such resources.8
12
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13. “
Googlebot caches aggressively in
order to reduce network requests
and resource usage. WRS may
ignore caching headers.8
13
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14. What does it mean?8
14
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15. main.js
Content fingerprinting8,9,10
main.2bb85551.js
15
main.js?version=2bb85551
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16. Does the website use content fingerprinting?8,9,10
16
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17. WRS does not retain state
across page loads8
17
Local Storage
Session Storage
Cookies
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18. JavaScript checklist part 28,9,10
JS files
caching
methods.
Content
relience on
Local
Storage,
Cookies
etc.
18
@Gaca-Tworek

19. JavaScript &
Performance
How JS can impact loading times and user experience?
3
19
@Gaca-Tworek

20. How does the browser
process JavaScript?11
Load Execute
Parse /
Compile
20
@Gaca-Tworek

21. Look beyond JS
files’ size.11
21
Source:
https://developers.google.com/web/fundamentals/performance
/optimizing-content-efficiency/javascript-startup-optimization
@Gaca-Tworek

22. 22
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23. Why is it
important?11
23
Source:
https://developers.google.com/web/fundamentals/performance
/optimizing-content-efficiency/javascript-startup-optimization
@Gaca-Tworek

24. Compression11,12,13
24
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25. How much of the code
remains unused?11,14,15
25
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26. JavaScript checklist part 3A
Check
parsing /
compiling
times.
Is only
essential JS
being
loaded?
Are JS files
compressed
?
26
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27. Is the code minimized?11
27
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28. <script src="script.js"></script>
<script async src="script.js"></script>
28
How can we load JS files better?16,17
<script defer src="script.js"></script>
@Gaca-Tworek

29. How to Third-Party scripts impact performance?18
29
@Gaca-Tworek

30. How to Third-Party scripts impact performance?18
30
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31. JavaScript checklist part 3B
31
Is the code
minimized?
Validate
Third-
Party
scripts.
How
efficiently
do we load
the files.
@Gaca-Tworek

32. Efficiency
is the key
32
@Gaca-Tworek

33. Any questions ?
You can find me at
◉ @Gaca-Tworek
◉ https://www.linkedin.com/in/barbaragaca
Thanks!
33

34. JavaScript Checklist
◉ Look for JS rendered content.
◉ Can Google render it?
◉ Is this content indexed?
◉ Does website require Cookies
etc. to load content?
◉ How JS files are being cached?
34
◉ How long does it take to parse /
compile our JS code?
◉ Are those files compressed?
◉ Is only essential JS being loaded?
◉ Is the code minimized?
◉ How efficiently do we load the
files?
◉ Validate Third-Party Scripts.
@Gaca-Tworek

35. References - part 1
1. Understand the JavaScript SEO
basics (Google, documentation)
2. The new evergreen Googlebot
(Google, 2019)
3. The new evergreen Bingbot
simplifying SEO by leveraging
Microsoft Edge (Bing, 2019)
4. Evaluating page experience for a
better web (Google,2020)
5. Google Webmaster Central office-
hours (Google, 2019)
35
6. Google Webmaster JavaScript SEO
office hours (Google, 2020)
7. The Ultimate Guide to JavaScript SEO
(Onely,2020)
8. Fix Search-related JavaScript
problems (Google, 2020)
9. Prevent unnecessary network
requests with the HTTP Cache
(Google, 2018)
10.Caching: Google Webmasters
JavaScript SEO office hours (Google,
2020)

36. References - part 2
11. JavaScript Start-up Optimization
(Google)
12. Next Generation Server
Compression With Brotli (Smashing
Magazine, 2016)
13.Boosting Site Speed Using Brotli
Compression (LinkedIn, 2017)
14.Code Splitting (Webpack tutorial)
15.Tree Shaking (Webpack tutorial)
36
16.Scripts: async, defer (JavaScript.info,
2019)
17. Efficiently load JavaScript with defer
and async (flaviocopes,2018)
18.How do I measure the impact of
third-party script on my page?
(Google)