React’s Core Principles

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:

Start Learning React from the comfort of your home

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:

• useEffect
• useLayoutEffect

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