In this technique, we use event listeners on the scroll, resize, and orientationChange events in the browser. The scroll event is an obvious one to check when the user scrolls the page. The resize and orientationChange events are equally important for lazy loading. The resize event occurs when the size of the browser window changes. The orientationChange event gets triggered when the device is rotated from landscape to portrait mode, or vice versa.
In such cases, the number of images that become visible on the screen will change. Therefore, we'll need to trigger a load for these images. When either of these events occur, we find all the images on the page that are to be lazy loaded and haven't been loaded yet. From these images, we check which ones are now in the viewport.
This is done using the image's top offset, the current document scroll top, and window height. If it has entered the viewport, we pick the URL from data-src attribute and put it in the src attribute. We also remove the class lazy that identifies the images to be lazily loaded for events that trigger later. Once all the images are loaded, we remove the event listeners.
Browsers consider the image type, network speed, and data-saver setting in the browser to decide this threshold, keeping in mind developer expectations and user experience. The scroll event is sent to an element when the user scrolls to a different place in the element. The parent element takes the property scroll-snap-type while the child element takes scroll-snap-align applying their own behavior to their respective elements.
Since the scroll-snap is a fairly new property, it does not work on the older versions of the browsers creating cross browser compatibility issues. But, fallbacks are available for the same with older properties in the queue and polyfills providing an environment to run newer properties on the older browsers. Applying this property to your web page will certainly give a boost to the reputation of the website and greater user experience. With millions of websites on the internet, scroll-snap provides a simple yet recognizable user experience which can create a huge difference for standing your website apart.
For example, if a user scrolls to half of the div box, the div box would automatically snap to the top of its edge . This process is similar to locking the viewport to a certain area of the webpage so that whenever the user is not in that area, the webpage automatically snaps to it. Scroll-linked animations are often based on scroll position. For such applications, scroll event listeners are polling for scroll position — if scroll position is within range of a target, perform a scroll-linked animation. This is contrary to Javascript's design methodology, which is to listen for events rather than poll for events.
Analogously, scroll-linked animations would listen for scroll position rather than check scroll position. The observer pattern, specifically IntersectionObserver is a durable technique that accomplishes just this. Roughly speaking, once a certain scroll position has been reached, the IntersectionObserver event handler is executed.
We describe in more detail and more precisely what it accomplishes below. This module displays a small subset of records just enough to fill the viewport and uses the same DOM elements as the user scrolls. This method is effective because the number of DOM elements are always constant and tiny irrespective of the size of the list. Thus virtual scroll can display an infinitely growing list of items in an efficient way. Before ResizeObserver, you had to attach a listener to the document's resize event to get notified of any change of the viewport's dimensions. In the event handler, you would then have to figure out which elements have been affected by that change and call a specific routine to react appropriately.
We just have to remember the parent property and the child's property and apply them to the appropriate elements. The following code demonstrates the scroll-snap feature with container element scrolling in the vertical direction and scroll-snap-align set as "start". But that would involve a scroll event listener, which is still a very expensive thing to add to your app. Scrolling is one of the most frequent actions your users perform, and executing JavaScript during those events makes it hard to maintain a solid 60 FPS scroll.
The UI becomes out of sync with the user's mouse/finger/stylus. But they're not supported yet in IE or Edge where you'd want a JS fallback approach anyway. In JavaScript, attaching an event listener to constantly fire a callback on scroll can be performance-intensive, and if used unwisely, can make for a sluggish user experience. This may seem complex at first, but this same behavior forms the basis of the technique for lazy loading background images.
In simple terms, we trick the browser into not applying the background image CSS property to an element till that element comes into the viewport. We attach the observer on all the images to be lazy loaded. Once this is done, we remove the lazy class from the image, and also remove the observer from that image. Many scroll events fire while you are scrolling a page or an element. If you attach an event listener to the scroll event, the code in the event handler needs time to execute. These interactive APIs would come with different functionalities that the developer can use to enhance the user experience and make the scrolling more native.
One such API is scrollTo about which I discussed in the Smooth Scroll CSS article. With scrollTo, the browser will automatically calculate the target element without providing any fixed number. It helps in cross-browser compatibility issues as it is a great choice for screens with different sizes. You can search for other similar APIs on GitHub and other platforms.
The scroll margin in the scroll-snap is used for giving the outset value on the container box. It is applied to the snapping elements and provides a margin between the edges of the container element and the child element. This property is most useful when the developer wants to provide different margin values to the different elements available.
If you want to provide the same margins in all the directions, it is better to use scroll-padding instead. Throttling focuses on the rate of execution and resolves the above pitfall. When an event is invoked repeatedly, the event handler is guaranteed to be executed every wait milliseconds. This has immediate applications with autocomplete in search. However, this method's pitfall is where debouncing thrives — if a burst starts and ends within waitmilliseconds, that burst will not trigger the event handler. For example, if wait is 1000ms second, and the user takes 500msto scroll past Section A of the webpage, Section A will never run its scroll-linked animation.
With the right combination of display and position misfortunes, this could offset the parallax effect adversely. Although this gives us a visibility-robust variant of discrete scrolling events, this does not encompass scroll-linked animations that occur continuously as the user scrolls. Several workarounds exist if a scroll event handler is necessitated in these scenarios. These methods generalize to all high-frequency event handlers and focus on reducing the number of times a handler is invoked. Here, i will give you very simple example of scroll to top in angular. Then i will simply add 100 items there and so you can scroll that div easily.
Bellow that div i will add one button call "Scroll to Top", when you click on it, it will scroll to top. More specifically, a list of 10,000 items cannot be shown all at once on the screen. We normally see a subview or "window" of the entire dataset in the limited screen real estate allocated to the UI component.
The rest will not be visible until the user scrolls to the appropriate position. We have covered almost everything related to lazy loading images in this guide. With faster loading pages comes a great user experience, something your visitors would love.
Often, users scroll swiftly through the page, and the image needs some time to load and appear on the screen. Lazy loading images that are not in the viewport improves initial page load performance and user experience. This is an in-depth guide to everything about lazy loading of images including native lazy loading methods. Note - All virtual-scroller events are emitted at the same time in response to its internal "refresh" function.
Some of these event emitters are bypassed if certain criteria don't apply. Scroll-snap-stop is an additional property in CSS which comes under the umbrella of the scroll-snap module. With scroll-snap-stop, the developer can force a snap-point to stop no matter how fast the scrolling happens. Call the update method to manually update existing scrollbars to accommodate new content or resized element. This method is by default called automatically by the script when the element itself, its content or scrollbar size changes. A function to call each time a type of element is added, removed or changes its size and scrollbar are updated.
Useful when you need to update the scrollbar automatically, each time a type of element is added, removed or changes its size. Make scrolling snap to a multiple of a fixed number of pixels. Useful in cases like scrolling tabular data, image thumbnails or slides and you need to prevent scrolling from stopping half-way your elements. Note that your elements must be of equal width or height in order for this to work properly. For horizontal scrollbar, the element should have a width (or max-width) value set.
Needless to say, these are properties to look out for but not to use, as of writing. However, proposals akin to this one hold the promise of further offloading scroll-linked animation work to the browser. Are not always to blame, because even sans effects or improper scroll event listeners still create headaches.
Twitter responded to a rash of issues with laggy scrolling in 2011, leading the creator of jQuery John Resig to conclude expensive scroll event handlers are a bad idea. Plotly_legendclick and plotly_legenddoubleclick allow customization of the plotly legend. The default behaviour of plotly_legendclick is to hide a trace and the default behavior of plotly_legenddoubleclick is to select one trace and hide all the others. We can add to the default behaviour by creating a new plotly_legendclick event with a function of our choice. We can also disable the default behaviour by creating a function that returns false.
In the example below, we do both in order to create a plotly_legendclick event which changes the marker color back to black instead of erasing the trace. Once we have our layout and styles, we're going to create the JavaScript functions to assign the class name to the elements when they scroll into view. We're also going to fade out the elements in JavaScript instead of CSS, as we want the elements to be visible in the event a browser does not have JavaScript enabled. NameTypeDefaultDescriptionvirtualboolean | VirtualOptionsEnables virtual slides functionality. Object with virtual slides parameters or boolean true to enable with default settings.
As we can see, using virtual scrolling technic, we can reduce rendering time quite significantly. 2 secs saving may not sound like much, and 10,000 items list may not sound like a common use case. But, in a real world application, we will often have multiple components. Individually, the rendering time for each component may not be much, but collectively, they often add up. If we can reduce rendering time for each component, the time savings will often lead to much more responsive UI.
It would not provide any significant benefit to the end user in terms of performance. The additional JS that you load on the page to enable lazy loading will offset any benefit reaped from lazy loading such a small number of images. One thing to note here is that the Javascript code for lazy loading is still the same. We are using the Intersection Observer API method with a fallback to the event listeners. Gets the elements available space relative to the closest scrollable ancestor. Right and bottom dimensions represent the distance to the respective edge of the viewport element, not the top and left edge.
If the element edge extends beyond the viewport, a negative value will be reported. As an example, take an app drawer with a large number of items that the user may have to scroll through. When they reach the bottom, the overflow container stops scrolling because there's no more content to consume. But notice what happens if the user continues to scroll.
Scrolling is taken over by the parent container; the main page itself in the example. The CSS overscroll-behavior property allows developers to override the browser's default overflow scroll behavior when reaching the top/bottom of content. The quickest way to achieve a responsive grid is to set the grid's containing div to a percentage. The scroll-snap-destination property defines the position at which the element would snap according to the viewport.
It has a very simple syntax which requires just to define the position. By using the scroll-padding with scroll-snap-type, the edges are not snapped but an offset is created which is equal to the scroll-padding value the user gives. So now if the user scrolls with high speed, the point where the scroll element should snap, it still will but leaving an offset from the above element. Scroll-snap-type property defines the type of behavior the developer wants to give to the scrolling container element. It contains two values that define the direction of the scroll and the behavior of the scroll.
As you can see, I'm using RxJS to create a cold stream from the source of scroll events. Then, when observing the Document, I watch for the Window's scroll events. And, when observing an overflow Element, I watch for the Element's scroll events. With the way the code is written now, a new percentage is calculated with every single scroll event.
Since the calculation requires an inspection of the DOM state, it is very likely that this is forcing repaints . Regardless, I tried to add a throttleTime() operator to the RxJS stream; but, I couldn't get it to work. As such, I'm just transforming the scroll events as they are emitting. Lately, Alligator.io has been coming up a lot in my Google searches when researching the Angular web development framework. Not only does Alligator.io have quality content, they also have a nice, clean site design. One of the little delighters that they have on their site is a progress bar the indicates how far through an article the user has scrolled.
