Here are React’s core principles — the concepts that define how React works under the hood and how you’re meant to build apps with it:
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1. Declarative UI
React uses a declarative approach — you describe what the UI should look like, and React updates the DOM to match.
- You don’t manually manipulate the DOM.
- You simply declare state → UI.
2. Component-Based Architecture
Everything in React is a component.
- Components are reusable, isolated pieces of UI.
- Each component manages its own structure, logic, and styling.
- Components can be nested and composed like building blocks.
3. Unidirectional Data Flow (One-Way Data Binding)
Data always flows from parent to child, not the other way around.
- Predictable data flow → easier debugging.
- Encourages clean architecture and state lifting.
4. Virtual DOM
React maintains a lightweight copy of the DOM.
- On state changes, React computes the minimal number of updates.
- Efficient re-rendering → faster UI performance.
5. Reconciliation
React’s algorithm (Fiber) determines what changed in the UI:
- Compares current UI tree vs new UI tree.
- Updates only the necessary parts.
This is what makes React fast and predictable.
6. JSX (JavaScript XML)
A syntax extension that lets you write UI markup directly inside JavaScript.
- Looks like HTML
- Compiles to React.createElement()
- Seamlessly mixes logic + UI
JSX is not required but is a core part of how React apps are built.
7. Hooks
Modern React uses hooks to manage:
- State (
useState) - Side effects (
useEffect) - Context (
useContext) - Lifecycle logic without classes
- Custom hooks for reusable logic
Hooks follow strict rules to keep components consistent.
8. State Management
State controls the interactive part of your UI.
- Local state using hooks
- Global state via context or external stores
- React rerenders components when state changes
9. Immutability
React encourages immutable updates:
- Don’t mutate objects/arrays directly.
- Create new copies on updates.
- Improves performance and predictability.
10. Composition Over Inheritance
React prefers composition, not class inheritance.
- Build features by combining components.
- Reuse functionality via props, children, hooks.
11. Props-Driven Communication
Props are how components talk:
- Parent → Child
- Pure and predictable
- No side effects
Functional purity makes UI more stable.
12. Pure Components / Pure Rendering
Given the same props and state, components should output the same UI.
- No hidden state mutations
- No inconsistent side effects
- Enables memoization optimizations
13. Side-Effects Are Isolated
React keeps rendering pure, and effects are separated using hooks like:
useEffectuseLayoutEffect
This keeps UI rendering predictable.
14. Server + Client Rendering Flexibility
React supports multiple rendering modes:
- CSR (Client-Side Rendering)
- SSR (Server-Side Rendering)
- SSG (Static Generation)
- RSC (React Server Components)
The core idea is: React components can run anywhere.
15. Concurrent Rendering
Modern React (with Fiber) can:
- Pause rendering
- Prioritize important updates
- Avoid blocking the main thread
This powers features like:
- Suspense
- Transitions
- Streaming server rendering
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