Month: January 2024

Over 50 thousand developers visit DavidWalshBlog every month from around the world to learn JavaScript tricks and fix problems in their code. Unfortunately, some of them have a slow experience on the site.

David tracks the performance of his Core Web Vitals and overall performance with . Recently, we noticed that his CLS performance score was trending pretty slow for both desktop and mobile users.

Wait, what is CLS?

(CLS) is one of the performance metrics. It doesn’t measure load time directly, instead it measures how much a page shifts while it is being loaded. You’ve definitely seen this and been annoyed by it. These shifts make a site feel slow to a user.

CLS and the rest of the Core Web Vitals are super important. Not only because they measure user experience, but also because they influence the pagerank of a site in search. And search traffic is life for bloggers, media sites, e-commerce stores, and pretty much everyone with a website.

If we can fix the site’s CLS problem, we’ll give readers a faster experience, and boost the search ranking so David can help even more people. Sounds like a great incentive, let’s figure it out.

Crashing with Google Lighthouse

To find a performance problem, many developers will use a tool like Google Lighthouse. I ran a Lighthouse report on David’s site, and here’s what I got.

A perfect score! Let’s pack it up and go home.

The trouble is that Google Lighthouse is a lie. Real users won’t have this performance. That score only represents a single test, from my lightning-fast computer, in the USA, on a fast broadband connection.

David’s real users come from all over the world, on varying devices and networks, and at all times of the day. Their performance experience is far from perfect. That’s why we need to get for the performance, otherwise we might never know that there is a problem.

Where are the CLS problems?

David has been writing for a long time and has hundreds of posts on his site. Request Metrics tracks the CLS score per page so we can zero-in on the problems.

The largest traffic page is the root page, and that has a good CLS. But many of his posts, like and have troubling CLS scores. We can also track the elements responsible for CLS, and for most of the posts its main > article > p. That means the first paragraph of the article is the thing shifting. Why would it do that?

What is common about these posts with the worst CLS scores? Images. Images are a very common cause of CLS problems because a browser doesn’t always know how big an image is until it’s downloaded. The browser assumes it’s 0x0 until it has the image, then shifts everything around it to make room.

Posts with lots of images would shift many times as each image was downloaded and the article shifted to make room for the new content.

Using images correctly for CLS

To avoid layout shifts when using images, we need to give the browser hints about how big the images will be. The browser will use these hints to reserve space in the layout for the image when it’s finished downloading.

<img src="/path/to/image" width="300" height="100" />

Notice that the width and height are specified as their own attributes — not part of a style tag. These attributes set both a base size of the image as well as the aspect ratio to use. You can still use CSS to make the image bigger or smaller from here.

Also notice that there is no px unit specified.

Image Sizes in WordPress

DavidWalsh.name is hosted on WordPress, where there are some built-in tools to do this. We can utilize to get the dimensions of images he’s using and add them to the markup.

Proving it works

David made the image changes a few days ago, and we’re already seeing an improvement. CLS has dropped 20% to 0.123. We’re real close to the “Good” range of CLS now.

There’s still some issues to sort out around fonts, but that will be a story for another time and another post.

If you’re looking to improve the real performance of your site, or worried about losing your SEO juice from Core Web Vital problems, have a look at . It’s got the tools to track your performance and actionable tips to actually fix the problems.

Plus it’s free, so it’s got that going for it.

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Ask any software engineer and they’ll tell you that coding date logic can be a nightmare. Developers need to consider timezones, weird date defaults, and platform-specific date formats. The easiest way to work with dates is to reduce the date to the most simple format possible — usually a timestamp. To get the immediate time in integer format, you can use Date.now:

const now = Date.now(); // 1705190738870

I will oftentimes employ Date.now() in my console.log statements to differentiate likewise console.log results from each other. You could also use that date as a unique identifier for an event in a low-traffic environment.

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User input from HTML form fields is generally provided to JavaScript as a string. We’ve lived with that fact for decades but sometimes developers need to extract numbers from that string. There are multiple ways to get those numbers but let’s rely on regular expressions to extract those numbers!

To employ a regular expression to get a number within a string, we can use d+:

const string = "x12345david";
const [match] = string.match(/(d+)/);
match; // 12345

Regular expressions are capable of really powerful operations within JavaScript; this practice is one of the easier operations. Converting the number using a Number() wrapper will give you the number as a Number type.

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Streaming services have revolutionized content delivery, sending linear media companies into a panic as they watch traditional cable services decay. “Cutting the cord” is a common practice these days, but the streaming landscape isn’t perfect. We’re a decade into streaming so I wanted to share my thoughts on the state of new media: first impressions, second thoughts, and the third degree!

• Netflix is king thanks to having first mover advantage, and making smart financial moves over the past six months, but Netflix’s content is unremarkable. Their recent wins are USA’s Suits and content licensed from Max…they need to do better…
• The biggest loser in the current streaming landscape is the sports fan. Want to watch American Football? You need YouTubeTV, Peacock, and Amazon Prime. Soccer fan? You need Peacock, ESPN Plus, Paramount Plus, and then AppleTV Plus if you care about MLS. Being a live sports fan is really, really expensive.
• The parent companies of HBO and Showtime killed their brands with “Max” and “Paramount Plus”. HBO’s brand name and fuzzy fade in are iconic; “Max” means nothing. Part of me died with this stupid brand change.
• Streaming services lured us in with no advertisements but they’ve learned that the ad tiers generate more revenue. Now they’re trying to price us out to get us to choose the cheaper, ad-driven tier. Smart business but I’ll pay more to avoid the ads.
• Apple has all the resources in the world but they treat their streaming service like everything else they do: offer an unremarkable product and skate off of name. Ted Lasso was good, as was Shrinking, but everything else is filler…
• …and charging for Killers of the Flower Moon during the holidays, then providing it for free once people are back to work, is an embarrassing money grab.
• Amazon doesn’t offer nearly enough in exclusive content. These tech companies are half in, half out.
• Warner Brothers Discovery licensing their content, especially the Marvel Comic Universe IP, to Netflix because they need quick cash feels like a self-own. How do you grow Max by giving your best content to a better service?
• AppleTV’s hardware is insanely elegant to use, though I’m annoyed they didn’t commit to their gaming offering. Roku still feels like a Super Nintendo in a N64 world.
• The free streaming options these days are awesome if you don’t want to spend money. YouTube, RokuTV, and Tubi provide loads of great content at no expense.
• Disney Plus offer loads of great old movies but my kids rarely watch it — they’re busy watching cringe shows on Netflix…
• One huge frustration is the lack of a “previous” button that cable remotes had. Navigating between channels in YouTubeTV is painful…
• …and to further improve the experience, it would be great if AppleTV and Roku would allow users to have two apps side by side; let us build our own multi-view.
• Part of me wants to bin off all of my sports streaming services and simply use StreamEast…but the convenience is just too nice.

Agree or disagree? What did I miss? Let me know in the comments below!

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