Contant Optimization
Minimize HTTP Requests
Reducing component downloads improves page load times. Combine files and use CSS sprites to decrease requests. Base64 encoding for images increases HTML size but can be cached in stylesheets.
Reduce DNS Lookups
DNS resolution adds latency. Limit unique hostnames to 2-4 domains to balance DNS lookups and parallel downloads.
Avoid Redirects
301/302 responses delay rendering. Fix trailing slash issues and use CNAME records for domain changes instead of redirects.
Cache AJAX Responses
Make asynchronous responses cacheable with proper headers. Implement versioning through timestamps to avoid redundant requests.
Defer Component Loading
Prioritize critical rendering resources. Load non-essential elements like hidden content and animations after initial render.
Preload Components
Predictively fetch resources during browser idle time: unconditionally (global assets), conditionally (user action-based), or anticipatorily (pre-redesign).
Reduce DOM Elements
Complex DOM structures increase processing time. Simplify markup and use semantic elements. Aim for under 700 elements on content-rich pages.
Distribute Assets Across Domains
Serve static resources from 2-4 subdomains to maximize parallel downloads while minimizing DNS lookups.
Limit Iframe Usage
Iframes introduce rendering overhead. Reserve for third-party content requiring security sandboxing.
Eliminate 404 Errors
Broken requests waste resources. Verify asset links and external dependencies.
CSS Optimization
Avoid CSS Exprestions
Dynamic property evaluation impacts performance. Modern browsers deprecate this feature.
Prefer Link Over Import
Use <link> instead of @import to maintain parallel loading and proper rendering order.
Minimize Filters
IE-specific filters like AlphaImageLoader block rendering. Use PNG8 fallbacks instead.
Position Stylesheets in Head
Place CSS in <head> to enable progressive rendering and faster perceived load times.
JavaScript Optimization
Eliminate Duplicate Scripts
Redundant scripts cause unnecessary HTTP requests and execution overhead. Implement module systems to prevent duplication.
Minimize DOM Access
Cache element references and batch DOM modifications. Avoid layout-triggering operations in JavaScript.
Implement Event Delegation
Attach single event listeners to parent elements instead of individual handlers for child elements.
Place Scripts at Bottom
Position non-critical JavaScript before </body> to prevent download blocking.
Asset Handling
Externalize CSS and JavaScript
Serve static assets as separate cacheable files rather then inline code.
Minify Assets
Remove comments and whitespace from CSS/JavaScript. Use tools like UglifyJS and CSSNano.
Optimize Images
Convert GIFs to PNGs, run compression tools, and use appropriate formats. Properly size images instead of HTML scaling.
Optimize Sprites
Arrange images horizontally, reduce color depth to PNG8, and minimize transparent areas.
Manage Favicon
Keep favicon under 1KB with proper caching headers.
Cookie Management
Minimize Cookie Size
Remove unnecessary cookies and set optimal domain scope and expiration.
Serve Static Assets Cookie-Free
Host static resources on separate domains without cookies to reduce request overhead.
Mobile Optimization
Limit Component Size
Keep assets under 25KB uncompressed for mobile cache compatibility.
Bundle Resources
Combine components into multipart documents where supported by user agents.
Server Optimization
Enable Gzip Compression
Compress text-based resources using Content-Encoding: gzip.
Avoid Empty Image Sources
Prevent unnecessary requests from blank src attributes in HTML or JavaScript.
Configure ETags
Implement entity tags for efficient resource validation compared to Last-Modified headers.
Use GET for AJAX
Prefer GET over POST for AJAX requests when possible due to single-packet transmission.
Flush Early
Send partial HTML responses during server processing to enable parallel browser operations.
Implement CDN
Distribute static assets geographically to reduce latency.
Set Cache Headers
Use Expires (static) and Cache-Control (dynamic) headers to maximize caching efficiency.