What are best practices for building scalable SaaS applications in ReactJS?

Question

ICSM · Answer

Building a scalable, long-lived SaaS frontend in React is less about clever patterns and more about
discipline, constraints, and boring consistency. Below are best practices that have proven to work in
real-world SaaS products that evolve for years with large teams.
I’ll structure this around your four focus areas and explicitly call out 
common mistakes to avoid.
1. Component Organization and State Management
1.1 Use Feature-Based Folder Structure (Not Type-Based)
Avoid
/components
/hooks
/services
/pages
This collapses as the app grows.
Prefer
/features
  /billing
    BillingPage.tsx
    BillingForm.tsx
    billing.api.ts
    billing.slice.ts
    billing.types.ts
  /auth
  /users
/shared
  /ui
  /hooks
  /utils
/app
  store.ts
  router.tsx
Why
Each feature is isolatedEasier refactoringNew engineers can reason locallyScales linearly with product growth
This is the #1 architectural decision that separates hobby apps from SaaS platforms.
1.2 Clear Component Responsibility Layers
Use three component tiers:
Page components
Routing-awareData fetchingCompose features
Feature components
Business logicDomain-specific UITalks to state/store
Shared UI components
Buttons, Modals, InputsZero business logic
Rule of thumb
If a component knows what product feature it belongs to, it is 
not reusable UI.
1.3 Treat Global State as a Scarce Resource
Best practice
Local state → useState, useReducerServer state → React Query / TanStack QueryGlobal client state → Redux Toolkit / Zustand
Anti-pattern
Putting server data into Redux
Instead
// Server state
useQuery(['users'], fetchUsers)
// Client state
useAuthStore()
useUIStore()
Rule
If the backend is the source of truth → it does not belong in Redux.
1.4 Slice State by Domain, Not UI
Bad
uiSlice
formSlice
tableSlice
Good
authSlice
billingSlice
organizationSlice
permissionsSlice
This mirrors backend bounded contexts and scales naturally.
2. Performance at Scale
2.1 Design for Renders, Not Micro-Optimizations
Most performance problems come from:
Over-lifting statePassing unstable propsDerived state inside render
Best practices
Keep state as close as possible to where it’s usedPrefer derived data via selectorsUse useMemo and useCallback only when measurable
Premature memoization is worse than no memoization.
2.2 Virtualize Everything That Grows
Mandatory for SaaS dashboards
TablesLogsActivity feeds
Use:
react-windowreact-virtualized
Never render 1,000+ rows directly.
2.3 Split by Routes, Not Components
Correct
const BillingPage = lazy(() =andgt; import('./BillingPage'))
Incorrect
lazy(() =andgt; import('./Button'))
Route-level code splitting gives 90% of benefits with 10% complexity.
2.4 Measure Before Optimizing
Use:
React ProfilerWeb Vitals (LCP, TTI)Why-Did-You-Render (dev only)
Rule
No performance fix without measurement.
3. Structuring Code for Ongoing Feature Development
3.1 Treat Frontend as a Product, Not a UI
Long-lived SaaS frontends:
Have versioned APIsHave domain modelsEnforce breaking-change discipline
Use:
Typed API layersDTO → domain mappingExplicit contracts
// user.mapper.ts
export function mapUser(dto: UserDTO): User {
  return {
    id: dto.id,
    fullName: `${dto.first_name} ${dto.last_name}`
  }
}
Never spread backend DTOs across components.
3.2 Centralize Side Effects
Bad
useEffect(() =andgt; {
  fetch()
  analytics.track()
  websocket.connect()
}, [])
Good
API layerEffect handlersDedicated services
This improves testability and onboarding.
3.3 Enforce Boundaries with Tooling
Use:
ESLint boundariesPath aliasesImport rules
Example:
features/* cannot import from other features directly
This prevents architectural decay over time.
3.4 Document Architecture Decisions
Maintain:
/docs/architecture.mdADRs (Architecture Decision Records)
This matters more in year 3 than year 1.
4. Common React Architecture Mistakes in SaaS
Mistake 1: “Redux for everything”
Leads to:
Bloated reducersHard refactorsTight coupling
Mistake 2: Over-abstracted hooks
useSuperGenericHookThatDoesEverything()
Good hooks are boring and specific.
Mistake 3: Component inheritance
React scales with composition, not inheritance.
Mistake 4: No domain modeling
UI logic leaks everywhere, making features expensive to change.
Mistake 5: Ignoring frontend migrations
React 18+, Suspense, server components — plan upgrades intentionally.
5. Real-World SaaS Lessons (What Teams Learn the Hard Way)
From teams building serious SaaS platforms (including the type you referenced):
Frontend complexity grows faster than backend“Temporary” shortcuts live foreverStrong conventions matter more than clever codeMost bugs come from unclear state ownershipScaling teams is harder than scaling code
Recommended Baseline Stack for SaaS React
Concern
Recommendation
State
React Query + Redux Toolkit / Zustand
Routing
React Router (data APIs if possible)
API
Typed fetch layer (OpenAPI or manual)
Styling
CSS Modules / Tailwind (consistent choice)
Testing
RTL + Playwright
Linting
ESLint + architectural rules
Final Advice
If your goal is long-term SaaS stability:
Optimize for clarity, boundaries, and boredom.
The best React SaaS codebases:
Look unsurprisingAre easy to delete code fromCan onboard new engineers quickly
and

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What are best practices for building scalable SaaS applications in ReactJS?

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Can you answer this question?

1 Answers

1. Component Organization & State Management

1.1 Use Feature-Based Folder Structure (Not Type-Based)

1.2 Clear Component Responsibility Layers

1.3 Treat Global State as a Scarce Resource

1.4 Slice State by Domain, Not UI

2. Performance at Scale

2.1 Design for Renders, Not Micro-Optimizations

2.2 Virtualize Everything That Grows

2.3 Split by Routes, Not Components

2.4 Measure Before Optimizing

3. Structuring Code for Ongoing Feature Development

3.1 Treat Frontend as a Product, Not a UI

3.2 Centralize Side Effects

3.3 Enforce Boundaries with Tooling

3.4 Document Architecture Decisions

4. Common React Architecture Mistakes in SaaS

Mistake 1: “Redux for everything”

Mistake 2: Over-abstracted hooks

Mistake 3: Component inheritance

Mistake 4: No domain modeling

Mistake 5: Ignoring frontend migrations

5. Real-World SaaS Lessons (What Teams Learn the Hard Way)

Recommended Baseline Stack for SaaS React

Final Advice

Liked By

Concern	Recommendation
State	React Query + Redux Toolkit / Zustand
Routing	React Router (data APIs if possible)
API	Typed fetch layer (OpenAPI or manual)
Styling	CSS Modules / Tailwind (consistent choice)
Testing	RTL + Playwright
Linting	ESLint + architectural rules