Understanding Components, Instances, React Elements, and the DOM in React

When learning React, many developers get confused by terms like component, component instance, React element, and DOM element.

These concepts are closely related, but they are not the same.
Understanding the difference is important not only for learning React properly, but also for technical interviews.

Let’s break down in a simple way.

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1. Component – The Blueprint of the UI

A React component is usually a JavaScript function that returns JSX.

function Card() {
  return <h2>Hello World</h2>;
}

A component:

Defines how the UI should look

Does not directly appear on the screen

Acts like a blueprint or template

Think of a component as a design plan. Until you use it, nothing is rendered.

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2. Component Instance – The Living Version of a Component

When a component is used in JSX, React creates a component instance.

<Card />
<Card />

Each creates a separate instance.

Every component instance:

Has its own state

Has its own lifecycle

Lives independently in memory

This means multiple instances of the same component can exist at the same time, each behaving independently.

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3. React Element – A Description of the UI

A React element is what a component returns.

const element = <h2>Hello</h2>;

JSX is just syntactic sugar. Behind the scenes, it becomes:

React.createElement("h2", null, "Hello");

A React element:

Is a plain JavaScript object

Describes what should be rendered

Is immutable

Is not a DOM element

It is simply a lightweight description of the UI.

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4. DOM Element – The Real HTML in the Browser

DOM elements are the actual HTML elements rendered by the browser.

<h2>Hello</h2>

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React does not directly manipulate the DOM every time something changes.
Instead, it:

1. Creates a Virtual DOM

2. Compares changes (diffing)

3. Updates only the necessary parts of the real DOM

This approach makes React applications fast and efficient.

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How Everything Works Together

Here’s the complete flow:

Component
   ↓
Component Instance
   ↓
React Element (JSX)
   ↓
Virtual DOM
   ↓
Real DOM (Browser HTML)

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Final Summary

Component → A function that defines UI structure

Component Instance → A rendered, independent version of a component

React Element → A JavaScript object describing the UI

DOM Element → The actual HTML displayed in the browser

Once you understand this flow, many React concepts start to make much more sense — and interview questions become much easier to answer.