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Lazy Loading

Definition
Lazy Loading is a technique used to defer the loading of certain webpage elements—such as images, videos, or iframes—until the moment they become visible in a user’s browser or until a crawler actually reaches them. This approach helps to reduce initial page load times by only loading resources that are immediately needed.

What is it?
When a page deploys lazy loading, images and other media beyond the visible viewport are replaced with small placeholders. These placeholders become fully loaded assets only as the user scrolls closer or interacts with specific elements. For ecommerce sites with numerous product listings, lazy loading is particularly beneficial, as it prevents browsers from downloading large media files all at once, thereby speeding up initial rendering. Search engine crawlers can also encounter lazy-loaded elements in a more efficient manner, though care must be taken to ensure that essential content is still accessible and properly indexed.

How is it used?
Developers implement lazy loading using various JavaScript libraries or built-in browser features. Typically, a small script monitors the user’s viewport and triggers the loading of images or other resources once they come into view. This gradual approach improves performance metrics like Time to Interactive (TTI), reduces bandwidth usage, and can enhance user experience by making pages feel more responsive. For SEO, ensuring that lazy-loaded content is crawlable—often by using semantic markup and fallback mechanisms—helps maintain search engine visibility.

Applicable Areas

Related terms

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