Unlock the Power of Lazy Loading in JavaScript

What is Lazy Loading?

Lazy loading is a technique that defers the initialization of an element or object until it’s needed. This means that a target DOM element becomes visible and loads only when a user scrolls through it on a webpage, reducing the initial page load time and improving performance.

The Importance of Lazy Loading

Neglecting to lazy load can lead to a huge lag in page performance, low user retention, and a large impact on web performance and accessibility. By implementing lazy loading, you can reduce page size, memory footprint, and general load time, making your platform more accessible and user-friendly.

Native Lazy Loading API

The native lazy loading API is built on top of the Intersection Observer API, which detects when an element becomes available or visible inside the browser’s viewport. With this API, you can know when two DOM elements intersect and trigger a handler function to handle other parts of your code logic.

Creating an Intersection Observer

To create an intersection observer, you need to listen to the occurrence of an intersection observer event and trigger a callback function or handler to run when this kind of event occurs. The intersection observer event is a browser event that includes the DOMContentLoaded event.

const observer = new IntersectionObserver((entries) => {
  // Trigger a callback function when the element intersects with the viewport
}, {
  // Options object for the target element
  root: null,
  threshold: 1.0,
});

Implementing Lazy Loading

Lazy loading can be implemented using the default browser attribute or the intersection observer. The default browser attribute involves using the loading attribute on <img> and <iframe> HTML elements and setting it to “lazy” to let the browser know to load the element as it approaches the viewport.

<img src="image.jpg" loading="lazy">
<iframe src="iframe.html" loading="lazy"></iframe>

The intersection observer involves customizing the options object for the target element and triggering a callback function when the target element intersects with a parent element.

observer.observe(document.getElementById('target-element'));

What Other Page Resources Can Use Lazy Loading?

Lazy loading is not limited to images. Other page resources that can benefit from lazy loading include:

• JavaScript: By splitting JavaScript code into smaller modules
• CSS: By writing modular CSS code
• Inline frames (iframes): By setting the loading attribute to “lazy”

Lazy Loading Best Practices

When implementing lazy loading, it’s essential to:

1. Identify the elements to lazy load
2. Set up the intersection observer
3. Implement the lazy loading logic
4. Use appropriate loading attributes
5. Provide fallback content

Additionally, consider the scenarios where lazy loading is not suitable, such as:

• Critical resources
• Small or fast-loading resources
• SEO considerations