Placeholder image is loaded at page load (left), and when scrolled into the An example of image lazy loading in action. Page load, and replaces them with lazily-loaded images as they're scrolled into Medium, which loads lightweight placeholder images at The placeholder image is suddenly replaced by the final image.Īn example of image lazy loading can be found on the popular publishing platform.At some point, you scroll a placeholder image into the viewport.You arrive at a page, and begin to scroll as you read content.You've probably already seen lazy loading in action, and it goes something like Identify off screen images, which are candidates for lazy loading. Improvement, you may have seen some guidance in this realm in the form of theĭefer offscreen images audit: One of Lighthouse's performance audits is to If you've used Lighthouse and examined some opportunities for Where images are concerned, "non-critical" is often synonymous with Instead, these non-critical resources are loaded at the moment of Lazy loading is a technique that defers loading of non-critical resources at page Unfortunately, project stakeholders may be unwilling to cut any media resources from their existingĮspecially when all parties involved want to improve site performance,įortunately, lazy loading is a solution that lowers initial page payload and Images using this markup pattern: document.Typical payload of a website can be significant. Now let's see how to use Intersection Observer in JavaScript to lazy-load The data-src and data-srcset attributes, which are placeholder attributesĬontaining the URL for the image you'll load once the element is in the viewport.The src attribute, which references a placeholder image that will appear when.The class attribute, which is what you'll select the element with in.There are three relevant pieces of this markup that you should focus on: Let's assume this basic markup pattern for your lazily loaded elements: ![]() That's left to do is to decide what to do when an element is visible. Intersection Observer is easier to use and read than code relying on variousĮvent handlers, because you only need to register an observer to watchĮlements rather than writing tedious element visibility detection code. Most compatible across browsers, modern browsers offer a more performant andĮfficient way to do the work of checking element visibility via the If you've written lazy loading code before, you may have accomplished your taskīy using event handlers such as scroll or resize. Populated with URLs to the desired image content. If they are, their src (and sometimes srcset) attributes are To polyfill lazy loading of elements, we use JavaScript to check if they're in the To learn more, check out Browser-level lazy loading for the web. You will need to combine this with one of the methods explained next. If you have large numbers of images and want to be sure that users of browsers without support for lazy loading benefit If the browser does not support lazy loading then the attribute will be ignoredĪnd images will load immediately, as normal.įor most websites, adding this attribute to inline images will be a performance boostĪnd save users loading images that they may not ever scroll to. We suggest not to lazy-load iframes using the loading attribute until it becomes part of the specification. ![]() While implemented in Chromium, it does not yet have a specification and is subject to future change when this does happen. This attribute can be added to elements, and also to elements.Ī value of lazy tells the browser to load the image immediately if it is in the viewport,Īnd to fetch other images when the user scrolls near them. Which may be used in combination for the best compatibility across browsers:Ĭhrome and Firefox both support lazy loading with the loading attribute. With inline images we have three options for lazy loading, The most common lazy loading candidates are images as used in elements. In this post you will find out how to lazy-load both types of image. Images can appear on a webpage due to being inline in the HTML as elements
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