JSX vs HTML differences in React - Performance Comparison

Performance: JSX vs HTML differences

MEDIUM IMPACT

This affects how the browser parses and renders UI elements, impacting initial load and update speed.

Rendering UI elements in React

React

const element = <div className="container">Hello</div>; ReactDOM.render(element, root);

JSX compiles to React.createElement calls, enabling React to build a virtual DOM efficiently and update only changed parts.

📈 Performance GainSingle virtual DOM creation, minimal reflows, faster updates

Rendering UI elements in React

React

const htmlString = '<div class="container">Hello</div>'; ReactDOM.render(<div dangerouslySetInnerHTML={{__html: htmlString}} />, root);

Passing raw HTML strings requires React to dangerously set innerHTML, causing slower parsing and potential security risks.

📉 Performance CostBlocks rendering while parsing HTML string, triggers extra DOM parsing and potential reflows

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Raw HTML string in React	Direct DOM insertion	Multiple reflows if content changes	High paint cost due to full DOM updates	[X] Bad
JSX with React.createElement	Virtual DOM diffing minimizes DOM ops	Single reflow on updates	Lower paint cost by updating only changed nodes	[OK] Good

Rendering Pipeline

JSX is compiled to JavaScript calls that create virtual DOM nodes. React compares these nodes to update the real DOM efficiently, reducing costly layout and paint operations.

→Parsing

→Virtual DOM Creation

→Diffing

→Layout

→Paint

⚠️ BottleneckParsing raw HTML strings and updating DOM directly

Core Web Vital Affected

LCP

This affects how the browser parses and renders UI elements, impacting initial load and update speed.

Optimization Tips

1Always use JSX in React to leverage virtual DOM for efficient updates.

2Avoid inserting raw HTML strings directly to prevent extra parsing and reflows.

3JSX improves Largest Contentful Paint by reducing direct DOM manipulations.

Performance Quiz - 3 Questions

Why is using JSX better than raw HTML strings in React for performance?

A JSX compiles to virtual DOM calls that minimize direct DOM updates

B JSX loads faster because it is plain HTML

C Raw HTML strings are faster because they skip React

D JSX reduces network requests

DevTools: Performance

How to check: Record a React render and look for scripting and rendering times; compare raw HTML string insertion vs JSX component render.

What to look for: Long scripting times and forced reflows indicate raw HTML string usage; efficient virtual DOM updates show shorter scripting and paint times.