Technical SEO Nightmares with React Client-side Web Apps – Brighton SEO October 2025.pdf

In this talk, Simone lifts the lid on how JavaScript affects what search engines actually see - starting from the basics of indexation, then diving into a site migration gone sideways due to a dodgy client-side routing configuration in a React app.

It’s one for the technically curious: think rendering quirks, indexing bottlenecks, and sharp lessons from the technical SEO front lines.

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Discovered –Currently Not Indexed

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Duplicate, Google Chose another Canonical
/:/gamma-
a4/a4-all-
road/
/:/a4/a4-all-
road/

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WhatWeCover Today…
Simone De Palma
3 How Does React Routing Works
4 React & Tech SEONightmares
2 How JavaScript (Still) Affect SEO
1 JavaScript: the Genesis of UX
SEODepths.com

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JavaScript: the Genesis of UX
Part 1
Simone De Palma SEODepths.com

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JavaScript is a
Babylon of
Programming
Frameworks

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From One
Language,
Many Accents

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Mobile Apps have boomed since 2015
Forbes (2015). 2015 Is The Year Of The Mobile Web - Is Your Website Ready?

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SEO Specialist
Marketer

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90's -00's Around2015
<span>
<div>

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JavaScript isnotthe Villain
PoorBusiness Decisionsare

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Whatabout
React ?

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A JavaScript library for high-end
SPAs and mobile apps
Recycle UI components
Update content efficiently
Feeds with a solid ecosystem of JavaScript frameworks (like Redux, Next.js)
Build mobile apps (React Native) or server-rendered sites

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Crawl/Indexing
URLs
Change
URLsDon’tChange
Page Load Time Jarring Fast
User ExperienceLimited Excellent
Rendering SSR isEasy Default CSR
React doesn’t help with SEO

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eCommerce Currency Selector
React vs HTML ft. plain JavaScript

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React

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Simple JavaScript on top of HTML

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Are you saying we must have an HTML
solution for each page template?

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“We don’t have enough
bandwidth to handle the
request”
“We’re going to run this in
the next sprint”
“We need to get back to the
CMS to grant access to the
pipeline”

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Technical
Complexities
Poor
Management
No Money
Business Decisions
Complex Back-Ends

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•Why are we using aJavaScript library for
amostly static site?
•Why isn’t this justHTML?
•How does SEO feed into the Marketing
strategy?
•What’s the SEO value as a Marketing
Touchpoint?

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How JavaScript(Still) AffectSEO
Part 2
Simone De Palma SEODepths.com

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Google’s improved
JavaScript
execution
And yetstill…
Googlebot Users

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Excessive Client-
side JavaScript can
Break Rendering
Googlebot’s View

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LLMs can’texecuteJavaScript
But fetch contentfrom SSR sections

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JavaScript & the Indexing Pipeline
The Renderer is the Battlefield

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JavaScript abide by their own Rules
But can be Mitigated

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How Does React RoutingWork
Part 3
Simone De Palma SEODepths.com

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Routing in React

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Server-Side Routing & Traditional Web Apps

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Excellent for crawling, rendering, and
indexation
Faster initial load time
Slower progressive navigation as it
needs dependencies
Frontend and backend are tied
together

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Client-Side Routing & SPAs

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Seamless navigation
Frontend and backend are separated
Slower initial load time
Search engines can’t crawl/render
critical components

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What to look For
InvisibleInternalLinks
Rendering Blocks

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How to look for
Wappalyzer

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React For SEO
Download for Free

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Does it Affect Rendering?
Rendering DifferenceEngine URL InspectionTool

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React & Tech SEONightmares
Part 4
Simone De Palma SEODepths.com

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The Router in React
Router
URL Routing

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That Beautiful Typo in the Router…

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… caused Indexation to go rogue

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… making it harder to Crawl
Filter Selection doesn’t
update the URL

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But the page loaded just fine!
Filter Selection doesn’t
update the URL

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Default Client-side Routing
The server didn’t receive any requests
to update the pages
Indexing

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Filter banner
missing
Product
listings
missing
… as well as
Rendering
impediments

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Default Client-side Rendering
The banner filter and product
listings were hydrated client-side
Rendering

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TL;DR –Client-Side Stuff Poisons SEO

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Our Ask #1
Fix Duplicate Keys with
Dynamic Filtering in the
Router

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Nobody said it
was Easy

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#2 Switch to Server-Side Routing

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But stitching up the front-end to the
back-end was
??????Resource-intensive
Expensive

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Static Server
Generation for
static pages
Server-Side
Rendering for
dynamic filtering
Pre-Rendering #3
Expensive and Ineffective

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Because React is
a Different Beast

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Align your SEO strategy to
Marketing goals…
#1 That Key Takeaway

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…based on your CSR Reliance

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Keep off
Client-side
Routing &
Rendering
#2 That Key Takeaway

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Advocate
Server-side
Routing &
Rendering
#3 That Key Takeaway

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From SPA to Micro Frontends
SPA
React
Dynamic
Filtering
Filtered View
Web app Layer
Service Layer
Dynamic Filtering
SPA
React
Listings
Product Listings
Product Listings

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ManyThanks and…
Simone De Palma
GET THE
SLIDES
SEODepths.com