What is a component in React - Visual Explanation

Concept Flow - What is a component

Start React App

↓

Define Component

↓

React Calls Component Function

↓

Component Returns JSX

↓

React Converts JSX to DOM Elements

↓

DOM Elements Rendered in Browser

↓

User Sees UI from Component

This flow shows how React uses a component function to create UI elements that appear in the browser.

Execution Sample

React

function Greeting() {
  return <h1>Hello, friend!</h1>;
}

// Usage in JSX
<Greeting />

A simple React component called Greeting returns a heading that says 'Hello, friend!'.

Execution Table

Step	Action	Evaluation	Result
1	React calls Greeting function	Greeting() runs	Returns JSX <h1>Hello, friend!</h1>
2	React converts JSX	JSX transformed	Creates DOM element <h1>
3	React inserts DOM element	DOM updated	Browser shows heading with text 'Hello, friend!'
4	User views page	UI visible	User sees 'Hello, friend!' on screen

💡 Component function returns JSX, React renders it, and UI appears; no further steps.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
Greeting	function defined	called	returns JSX	JSX converted	DOM rendered

Key Moments - 2 Insights

Why does the Greeting function return JSX instead of HTML?

JSX looks like HTML but is JavaScript syntax that React understands to create UI elements, as shown in execution_table step 1 and 2.

When does the user actually see the text 'Hello, friend!'?

After React converts JSX to DOM and inserts it into the page (execution_table steps 3 and 4), the user sees the text.

Visual Quiz - 3 Questions

Look at the execution table, what does the Greeting function return at step 1?

A JSX <h1>Hello, friend!</h1>

B Plain text 'Hello, friend!'

C DOM element <h1>

D Nothing

💡 Hint

Check the 'Result' column in step 1 of the execution_table.

At which step does React convert JSX into a DOM element?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Action' and 'Evaluation' columns in execution_table step 2.

If the Greeting function returned null instead of JSX, what would happen?

A React would render default text

B React would show an error

C React would render nothing on the page

D React would crash

💡 Hint

Think about what React renders when a component returns no JSX, related to execution_table step 1.

Concept Snapshot

React component is a function that returns JSX.
JSX looks like HTML but is JavaScript.
React calls the component to get JSX.
React converts JSX to DOM elements.
DOM elements show UI in the browser.
Components build the UI piece by piece.

Full Transcript

A React component is a function that returns JSX, which looks like HTML but is actually JavaScript code. When React runs the component function, it gets JSX back. React then converts this JSX into real DOM elements that the browser can display. Finally, the user sees the UI created by these elements. This process happens every time React renders the component. Components help build the user interface in small, reusable pieces.