- name
- best-practices
- description
- Apply modern web development best practices for security, compatibility, and code quality. Use when asked to "apply best practices", "security audit", "modernize code", "code quality review", or "check for vulnerabilities".
- license
- MIT
- metadata
- {"author":"web-quality-skills","version":"1.0"}
# Best practices
Modern web development standards based on Lighthouse best practices audits. Covers security, browser compatibility, and code quality patterns.
## Security
### HTTPS everywhere
**Enforce HTTPS:**
```html
<!-- ❌ Mixed content -->
<img src="http://example.com/image.jpg">
<script src="http://cdn.example.com/script.js"></script>
<!-- ✅ HTTPS only -->
<img src="https://example.com/image.jpg">
<script src="https://cdn.example.com/script.js"></script>
<!-- ✅ Protocol-relative (will use page's protocol) -->
<img src="//example.com/image.jpg">
```
**HSTS Header:**
```
Strict-Transport-Security: max-age=31536000; includeSubDomains; preload
```
### Content Security Policy (CSP)
```html
<!-- Basic CSP via meta tag -->
<meta http-equiv="Content-Security-Policy"
content="default-src 'self';
script-src 'self' https://trusted-cdn.com;
style-src 'self' 'unsafe-inline';
img-src 'self' data: https:;
connect-src 'self' https://api.example.com;">
<!-- Better: HTTP header -->
```
**CSP Header (recommended):**
```
Content-Security-Policy:
default-src 'self';
script-src 'self' 'nonce-abc123' https://trusted.com;
style-src 'self' 'nonce-abc123';
img-src 'self' data: https:;
connect-src 'self' https://api.example.com;
frame-ancestors 'self';
base-uri 'self';
form-action 'self';
```
**Using nonces for inline scripts:**
```html
<script nonce="abc123">
// This inline script is allowed
</script>
```
### Security headers
```
# Prevent clickjacking
X-Frame-Options: DENY
# Prevent MIME type sniffing
X-Content-Type-Options: nosniff
# Enable XSS filter (legacy browsers)
X-XSS-Protection: 1; mode=block
# Control referrer information
Referrer-Policy: strict-origin-when-cross-origin
# Permissions policy (formerly Feature-Policy)
Permissions-Policy: geolocation=(), microphone=(), camera=()
```
### No vulnerable libraries
```bash
# Check for vulnerabilities
npm audit
yarn audit
# Auto-fix when possible
npm audit fix
# Check specific package
npm ls lodash
```
**Keep dependencies updated:**
```json
// package.json
{
"scripts": {
"audit": "npm audit --audit-level=moderate",
"update": "npm update && npm audit fix"
}
}
```
**Known vulnerable patterns to avoid:**
```javascript
// ❌ Prototype pollution vulnerable patterns
Object.assign(target, userInput);
_.merge(target, userInput);
// ✅ Safer alternatives
const safeData = JSON.parse(JSON.stringify(userInput));
```
### Input sanitization
```javascript
// ❌ XSS vulnerable
element.innerHTML = userInput;
document.write(userInput);
// ✅ Safe text content
element.textContent = userInput;
// ✅ If HTML needed, sanitize
import DOMPurify from 'dompurify';
element.innerHTML = DOMPurify.sanitize(userInput);
```
### Secure cookies
```javascript
// ❌ Insecure cookie
document.cookie = "session=abc123";
// ✅ Secure cookie (server-side)
Set-Cookie: session=abc123; Secure; HttpOnly; SameSite=Strict; Path=/
```
---
## Browser compatibility
### Doctype declaration
```html
<!-- ❌ Missing or invalid doctype -->
<HTML>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<!-- ✅ HTML5 doctype -->
<!DOCTYPE html>
<html lang="en">
```
### Character encoding
```html
<!-- ❌ Missing or late charset -->
<html>
<head>
<title>Page</title>
<meta charset="UTF-8">
</head>
<!-- ✅ Charset as first element in head -->
<html>
<head>
<meta charset="UTF-8">
<title>Page</title>
</head>
```
### Viewport meta tag
```html
<!-- ❌ Missing viewport -->
<head>
<title>Page</title>
</head>
<!-- ✅ Responsive viewport -->
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Page</title>
</head>
```
### Feature detection
```javascript
// ❌ Browser detection (brittle)
if (navigator.userAgent.includes('Chrome')) {
// Chrome-specific code
}
// ✅ Feature detection
if ('IntersectionObserver' in window) {
// Use IntersectionObserver
} else {
// Fallback
}
// ✅ Using @supports in CSS
@supports (display: grid) {
.container {
display: grid;
}
}
@supports not (display: grid) {
.container {
display: flex;
}
}
```
### Polyfills (when needed)
```html
<!-- Load polyfills conditionally -->
<script>
if (!('fetch' in window)) {
document.write('<script src="/polyfills/fetch.js"><\/script>');
}
</script>
<!-- Or use polyfill.io -->
<script src="https://polyfill.io/v3/polyfill.min.js?features=fetch,IntersectionObserver"></script>
```
---
## Deprecated APIs
### Avoid these
```javascript
// ❌ document.write (blocks parsing)
document.write('<script src="..."></script>');
// ✅ Dynamic script loading
const script = document.createElement('script');
script.src = '...';
document.head.appendChild(script);
// ❌ Synchronous XHR (blocks main thread)
const xhr = new XMLHttpRequest();
xhr.open('GET', url, false); // false = synchronous
// ✅ Async fetch
const response = await fetch(url);
// ❌ Application Cache (deprecated)
<html manifest="cache.manifest">
// ✅ Service Workers
if ('serviceWorker' in navigator) {
navigator.serviceWorker.register('/sw.js');
}
```
### Event listener passive
```javascript
// ❌ Non-passive touch/wheel (may block scrolling)
element.addEventListener('touchstart', handler);
element.addEventListener('wheel', handler);
// ✅ Passive listeners (allows smooth scrolling)
element.addEventListener('touchstart', handler, { passive: true });
element.addEventListener('wheel', handler, { passive: true });
// ✅ If you need preventDefault, be explicit
element.addEventListener('touchstart', handler, { passive: false });
```
---
## Console & errors
### No console errors
```javascript
// ❌ Errors in production
console.log('Debug info'); // Remove in production
throw new Error('Unhandled'); // Catch all errors
// ✅ Proper error handling
try {
riskyOperation();
} catch (error) {
// Log to error tracking service
errorTracker.captureException(error);
// Show user-friendly message
showErrorMessage('Something went wrong. Please try again.');
}
```
### Error boundaries (React)
```jsx
class ErrorBoundary extends React.Component {
state = { hasError: false };
static getDerivedStateFromError(error) {
return { hasError: true };
}
componentDidCatch(error, info) {
errorTracker.captureException(error, { extra: info });
}
render() {
if (this.state.hasError) {
return <FallbackUI />;
}
return this.props.children;
}
}
// Usage
<ErrorBoundary>
<App />
</ErrorBoundary>
```
### Global error handler
```javascript
// Catch unhandled errors
window.addEventListener('error', (event) => {
errorTracker.captureException(event.error);
});
// Catch unhandled promise rejections
window.addEventListener('unhandledrejection', (event) => {
errorTracker.captureException(event.reason);
});
```
---
## Source maps
### Production configuration
```javascript
// ❌ Source maps exposed in production
// webpack.config.js
module.exports = {
devtool: 'source-map', // Exposes source code
};
// ✅ Hidden source maps (uploaded to error tracker)
module.exports = {
devtool: 'hidden-source-map',
};
// ✅ Or no source maps in production
module.exports = {
devtool: process.env.NODE_ENV === 'production' ? false : 'source-map',
};
```
---
## Performance best practices
### Avoid blocking patterns
```javascript
// ❌ Blocking script
<script src="heavy-library.js"></script>
// ✅ Deferred script
<script defer src="heavy-library.js"></script>
// ❌ Blocking CSS import
@import url('other-styles.css');
// ✅ Link tags (parallel loading)
<link rel="stylesheet" href="styles.css">
<link rel="stylesheet" href="other-styles.css">
```
### Efficient event handlers
```javascript
// ❌ Handler on every element
items.forEach(item => {
item.addEventListener('click', handleClick);
});
// ✅ Event delegation
container.addEventListener('click', (e) => {
if (e.target.matches('.item')) {
handleClick(e);
}
});
```
### Memory management
```javascript
// ❌ Memory leak (never removed)
const handler = () => { /* ... */ };
window.addEventListener('resize', handler);
// ✅ Cleanup when done
const handler = () => { /* ... */ };
window.addEventListener('resize', handler);
// Later, when component unmounts:
window.removeEventListener('resize', handler);
// ✅ Using AbortController
const controller = new AbortController();
window.addEventListener('resize', handler, { signal: controller.signal });
// Cleanup:
controller.abort();
```
---
## Code quality
### Valid HTML
```html
<!-- ❌ Invalid HTML -->
<div id="header">
<div id="header"> <!-- Duplicate ID -->
<ul>
<div>Item</div> <!-- Invalid child -->
</ul>
<a href="/"><button>Click</button></a> <!-- Invalid nesting -->
<!-- ✅ Valid HTML -->
<header id="site-header">
</header>
<ul>
<li>Item</li>
</ul>
在 GitHub 查看