![]() ![]() The three relevant pieces of this markup are: the class attribute, and the data-src and data-srcset attributes. All that’s left to do for the developer is to decide what to do when an element is visible. Developers only need to register an observer to watch elements, rather than writing tedious element visibility detection code. Intersection Observer is easier to use and read than code relying on various event handlers. ![]() This is performed via the Intersection Observer API. However, modern browsers offer a more performant and efficient way to do the work of checking element visibility. This approach is the most compatible across browsers. If you’ve written lazy loading code before, you may have accomplished your task by using event handlers such as scroll or resize. These depend on how the page is scrolled, or the next section that the user could visit. There are a lot of techniques for lazy loading. Only download the essential images, and make a lazy loading of the other resources. One of the most widespread and useful bits of advice I’ve come across is to avoid having the browser download all the images when loading the page. A very small JS library allows you to use this element, even on unsupported browsers. Browsers like Internet Explorer 11 do not support this element. The syntax is very similar to the element and allows you to use the attributes that I first showed you for the element. The picture element is a great way to provide alternative sources for image files, so the browser can choose depending on device capabilities. This should not preclude us from using the most optimized format for most modern browsers. But not all browsers are able to support them - Internet Explorer, for example. There are different formats for optimizing images for the web, such as webpand jpg2000. Even in this case the syntax is really very simple: The picture element It can be automated or injected server-side. You’re putting CSS stuff in markup and you know how that goes. That can get a little complicated, and honestly it might be a little dangerous. You can use sizes to match your CSS layout exactly and tell the browser exactly how big that image is going to be on every screen size, matching how your breakpoints work in your design. The sizes attribute is used to avoid this problem and, therefore, to help the browser choose the most optimized image for that case. That’s usually not an awful assumption to make. But, the assumption is that the image should be displayed in full screen (100vw). The browser, in this case, will choose the image best suited to its resolution. With a very simple syntax, you can instruct the browser to decide which one of the different image sizes are needed: This is done through two attributes, srcset and sizes. The HTML5 element has been designed to give the developer the ability to optimize the images according to the screen resolution. It is an art because there is no one definitive answer.īut how we can optimize our images from mobile form in addition to using image magic or any other web optimization tool? The img element It is a science because there are many well developed techniques and algorithms that can significantly reduce the size of an image. Image optimization is both a science and an art. ![]() The fewer bytes the browser has to download, the less time the user will have to wait for the render of useful content on the screen. As a result, optimizing images can frequently yield some of the largest byte savings and performance improvements for your website. Images often account for most of the downloaded bytes on a web page and often occupy a significant amount of visual space. By Riccardo Canella An intro to responsive image optimization with HTML5 and Intersection Observer ![]()
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