JavaScript Performance: Optimize Your Code for Speed

Why JavaScript Performance Matters

JavaScript is often the biggest contributor to slow websites. It blocks rendering, consumes CPU, and affects all Core Web Vitals metrics.

Impact on Core Web Vitals

LCP: JS blocking delays content rendering

INP: Heavy JS causes slow interactions

TBT: Long tasks block the main thread

Bundle Optimization

Code Splitting

Load only what's needed:

``javascript

// Dynamic import

const Module = await import('./heavy-module.js');

`

Tree Shaking

Remove unused code:

`javascript

// Only imports used functions

import { used } from 'library';

`

Minification

Remove whitespace and comments

Shorten variable names

Use terser or esbuild

Loading Strategies

Defer Non-Critical JS

`html

`

Async for Independent Scripts

`html

`

Module Scripts

`html

`

Performance Patterns

Debounce/Throttle

Limit function execution frequency:

`javascript

const debounced = debounce(handler, 300);

``

Virtual Scrolling

Only render visible items in long lists.

Web Workers

Move heavy computation off main thread.

Analyze your JavaScript with our free performance audit tool.