What is eager loading? Difference between eager & lazy loading
It doesn’t really matter how visually aesthetic your website appears, if it takes time to load, your visitors will show you a clean pair of heels. With increasing Internet speeds, users’ expectations have also increased with respect to page load times. It doesn’t matter if the user is visiting a website via their smartphone or computer; they just want it to load quickly. Unfortunately, many websites are slow to load.
Now, the question that arises here is— Why do some sites take longer to load? This is primarily because the data on these sites including the images and videos embedded in them are larger in size. Bulky files, after all, take longer to load. And that is why if you want to drive and retain traffic, it’s important that you optimize the data loading process of your website.
There are basically two data loading strategies that affect the performance of a site— eager loading and lazy loading.
What is Eager Loading?
The name eager loading is pretty suggestive and it refers to an optimization technique for website or online content in the field of web development. Eager loading means that the content of a site including the embedded images and other elements will load all at once. It also permits the browser to cache the content, so that the page can directly load from the device the next time it is requested. However, if the website has considerably large files, then the elements will load slower even with this method.
If your website has more textual content and very few images, videos, and other large files, then you can go for the eager loading technique. It loads all assets at once without the need to run additional SQL queries. It doesn’t just save load time for lightweight websites but also reduces the number of queries.
You may have experienced eager loading before if you have visited a page with lots of videos or photos that displayed a loading screen. Eager loading kind of force-loads all of the assets on a webpage. It loads related entities, even though the visitor never scrolls down to them.
Although eager loading allows you to load all of your resources simultaneously, it can cause slower loading speeds and increase bandwidth usage.
The best example of eager loading would be Wikipedia. Since Wikipedia mostly contains textual content, its pages use the eager loading technique to load data.
The all-at-once method of eager loading works best in certain scenarios. What are they? Find out here
A user should be able to see everything “above the fold.” This fold is at the bottom of your web browser window. Users should see content within this area immediately upon page load. You can find the fold in various places depending on your screen size and window size. To use lazy loading, you might need to view your website from different devices and make the best judgement to decide where to lazy-load the content. That, however, might not always be possible. And that is why some prefer to play it safe by opting for eager loading.
You should make sure that any media or code running in the background of your webpage is loaded with eager loading. Web applications are an example. They require all functionality to be fully loaded before they are run.
If you don’t really require lazy loading, don’t use it. Lazy loading can cause your site to be less attractive for these reasons—
—Too much dynamic loading on your site can cause interruptions and disrupt your visitors’ experience.
—SEO can be hurt by hiding too many elements. Search engines won’t index certain content if it isn’t shown. Go through Google’s lazy-loaded content guide which will help you ensure that your website is correctly read.
—To implement lazy loading, your website’s code needs to be modified. These changes will require resources and/or time to be made and tested.
—A page that is brief and/or has a lot of lightweight content is best kept away from any kind of over-engineering.
What is Lazy Loading?
Lazy loading is also referred to as on-demand loading. Here, all the elements in a website are not simultaneously loaded; only the content which the site regards as the most vital is loaded first. With lazy loading, the performance of a website increases significantly as only the most important content is loaded at the outset, delaying the loading of the rest of the elements on the page. So essentially, the remaining content gets displayed only when the visitor needs it. Since the browser is loading the website in a phase-by-phase manner, making only a portion of the content visible to the user at a time, the time required to load the website gets significantly reduced.
Lazy loading is primarily used for its ability to conserve system resources and boost the performance and speed of a site.
This feature is probably familiar to many Instagram users. Next time you visit Instagram, notice how photos don’t load until you scroll down to see them.
Since Instagram is loaded with images, it uses the lazy loading technique to load faster by deferring the loading of images until needed. Only those images appear which are needed immediately.
Images that aren’t in the user’s window of view on the page are replaced with placeholder images until they are brought to the user’s viewpoint.
So, from the discussion above, we learn how eager loading is different from lazy loading.
Since most websites these days use multimedia content, eager loading is of little value
Hence, lazy loading is a preferred data loading method for many, and has been discussed in detail below—
Lazy loading can have a major positive impact on user experience, engagement, and search engine ranking.
Lazy loading is usually implemented by using JavaScript code, often via web development frameworks like Node.js and React.
Lazy loading is primarily used for its ability to conserve system resources and boost the performance and speed of a site.
This feature is probably familiar to many Instagram users. Next time you visit Instagram, notice how photos don’t load until you scroll down to see them.
Since Instagram is loaded with images, it uses the lazy loading technique to load faster by deferring the loading of images until needed. Only those images appear which are needed immediately.
Images that aren’t in the user’s window of view on the page are replaced with placeholder images until they are brought to the user’s viewpoint.
So, from the discussion above, we learn how eager loading is different from lazy loading.
What are the various pros and cons of lazy loading?
Before you decide to implement lazy loading, it is important to consider its pros and cons.
Here are the upsides—
- Lazy loading optimizes content delivery to simplify end-user experiences.
- Users can view the content quicker because much of the elements have been coded for deferred loading.
- You get faster page loads. Reduced page load times ensure higher conversions, engagement and revenues.
- This allows for lower bandwidth usage which can lead to cost savings.
- Server infrastructure costs are also lower.
- Network activity is decreased due to delayed initialization of page elements.
- Reduces hardware resources needed to process additional requests.
Here are the downsides—
- Might make the user wait—
As explained above, a lazy loading script does not wait for all images to be initialized before loading the page. Although this process speeds up the delivery of pages, it can cause image loading delays. For example, a user might arrive at an image placeholder only to be required to wait for the image to load.
What is the solution?
—Use an Intersection Observer API to detect images entering the viewport.
—You can add a margin to images. The rootMargin parameter can be used to define the margin.
—When the image is several hundred pixels from the viewport, you can start loading it. While it allows the browser to take longer to download the image, it gets displayed in the viewport without making the user wait.
- Image Decoding Delays—
Large image files can clog JavaScript’s main thread when they are loaded and then dropped into the document object modeling (DOM). This process decodes images and when decoding takes time, the user interface becomes slow.
What is the solution?
Before dropping files into the DOM, you can asynchronously decode them. This can reduce or prevent image decoding delays. Asynchronous decoding is not possible on all browsers or devices and can complicate lazy loading logic.
- The content sometimes gets shifted—
Browsers must render images according to their size in order to fit the layout. The browser must know the image’s size to do this. Lazy loading scripts delay rendering images and prevent the browser from determining their size.
Browsers must resize containers to fit images, as containers come with a default configuration of 0x0 pixels. This changes the layout of the page and causes other elements to shift. Because content shifting results in a poor user experience, this is indeed a problem.
What’s the solution?
To help browsers create containers, specify the height and width of containers in advance.
The container can be loaded ahead of time so that the image can quickly be loaded to the container according to its size without any content shifting.
Lazy loading best practices
- Don’t delay loading images at the top of your webpage. This includes header images and logos. These should be immediately visible to the user when the page loads.
- Because different internet enabled devices have different screen sizes, what gets displayed first in the user’s window is highly likely to vary. To determine which resource to load first and which to defer, you can consider the type of device your users are most likely to use.
- You should avoid lazy loading if the page doesn’t exceed 100kb or has fewer than five images.
Final words
The discussion above highlights the differences between lazy and eager loading, as well as how they impact a site’s speed. As a rule of thumb, you can use lazy loading for content-heavy websites. Eager loading, on the other hand, is best suited for sites with a lot of textual content.
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