Web Performance Optimization Techniques for 2023

Understanding Core Web Vitals

Google's Core Web Vitals have become the industry standard for measuring web performance. These metrics focus on three aspects of user experience: loading, interactivity, and visual stability.

In 2023, Google has introduced a new metric called Interaction to Next Paint (INP), which is expected to eventually replace FID as a more comprehensive measure of responsiveness. INP measures the time from when a user interacts with a page to when the browser next renders a frame, capturing the full interaction duration.

Advanced Image Optimization

Images often account for the largest portion of a webpage's size. Modern image optimization goes beyond simple compression to include next-gen formats, responsive delivery, and intelligent loading strategies.

Next-Gen Image Formats

Traditional formats like JPEG and PNG are being replaced by more efficient alternatives:

Responsive Images

Serving appropriately sized images based on the device's screen size and resolution is crucial for performance. Use the srcset and sizes attributes to provide the browser with multiple image options:

<img 
  srcset="image-320w.jpg 320w,
          image-480w.jpg 480w,
          image-800w.jpg 800w"
  sizes="(max-width: 320px) 280px,
         (max-width: 480px) 440px,
         800px"
  src="image-800w.jpg"
  alt="Responsive image example"
/>

Lazy Loading and LQIP

Load images only when they're about to enter the viewport to reduce initial page load time. Combine this with Low-Quality Image Placeholders (LQIP) to improve perceived performance:

<img 
  src="placeholder.jpg" 
  data-src="full-image.jpg" 
  loading="lazy" 
  alt="Lazy loaded image" 
/>

For more complex scenarios, consider using the Intersection Observer API to implement custom lazy loading logic.

Image CDNs and Automation

Modern image CDNs like Cloudinary, imgix, and Akamai Image Manager can automatically optimize, format, resize, and deliver images based on the requesting device and browser capabilities. These services can dramatically simplify image management while improving performance.

JavaScript Optimization Strategies

JavaScript is often the biggest contributor to interactivity issues. Optimizing JavaScript delivery and execution is essential for good Core Web Vitals scores.

Code Splitting

Rather than sending all JavaScript to the user at once, split your code into smaller chunks that can be loaded on demand. Modern bundlers like Webpack, Rollup, and esbuild make this straightforward:

// Dynamic import example
button.addEventListener('click', async () => {
  const module = await import('./feature.js');
  module.doSomething();
});

Tree Shaking

Tree shaking eliminates unused code from your bundle. Ensure you're using ES modules and a bundler that supports tree shaking to reduce your JavaScript payload:

// Import only what you need
import { specificFunction } from 'large-library';

// Instead of
import * as largeLibrary from 'large-library';

Script Loading Strategies

How you load scripts can significantly impact performance:

• async: Downloads the script without blocking HTML parsing and executes as soon as it's available
• defer: Downloads without blocking HTML parsing but waits to execute until parsing is complete
• module: Treats the script as an ES module, which is deferred by default

<script async src="analytics.js"></script>
<script defer src="app.js"></script>
<script type="module" src="module.js"></script>