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The Chrome team announced a new feature called Lite Pages that can be activated by flipping on the Data Saver option on an Android device:

Chrome on Android’s Data Saver feature helps by automatically optimizing web pages to make them load faster. When users are facing network or data constraints, Data Saver may reduce data use by up to 90% and load pages two times faster, and by making pages load faster, a larger fraction of pages actually finish loading

In 2015 there were 24,000 different Android devices, and each of them was capable of downloading images. And this was just the beginning. The mobile era is starting to gather pace with mobile visitors starting to eclipse desktop. One thing is certain, building and running a website in the mobile era requires an entirely different approach to images. You need to consider users on desktops, laptops, tablets, watches, smartphones and then viewport sizes, resolutions, before, finally, getting to browser supported … Read article

The first time I made an image responsive, it was as simple as coding these four lines:

img {
  max-width: 100%;
  height auto; /* default */
}

Though that worked for me as a developer, it wasn’t the best for the audience. What happens if the the image in the src attribute is heavy? On high-end developer devices (like mine with 16GB RAM), few or no performance problems occur. But on low-end devices? It’s another story.… Read article

It's entirely too common to make broad-sweeping statements about all websites. Jason Miller:

We often make generalizations about applications we see in the wild, both anecdotal and statistical: "Single-Page Applications are slower than multipage" or "apps with low TTI loaded fast". However, the extent to which these generalizations hold for the performance and architectural characteristics we care about varies.

Just the other morning, at breakfast an An Event Apart, I sat with a fellow who worked on a university website … Read article

The idea for this article sparked when Chris wrote this in Thank You (2018 Edition):

I almost wish our URLs had years in them because I still don't have a way to scope analytic data to only show me data from content published this year. I can see the most popular stuff from the year, but that's regardless of when it was published, and that's dominated by the big guides we've had for years and keep updated.

I have … Read article

Rik Schennink documents a system for being able to write CSS selectors that style a page when it has scrolled to a certain point. If you're like me, you're already on the lookout for document.addEventListener('scroll' ... and being terrified about performance. Rik gets to that right away by both debouncing the function as well as marking the event as passive.… Read article

In a bid to have web applications serve needs for different types of users, it’s likely that more code is required than it would be for one type of user so the app can handle and adapt to different scenarios and use cases, which lead to new features and functionalities. When this happens, it’s reasonable to expect the performance of an app to dwindle as the codebase grows.

Code splitting is a technique where an application only loads the code … Read article

I've definitely been guilty of thinking about rendering on the web as a two-horse race. There is Server-Side Rendering (SSR, like this WordPress site is doing) and Client-Side Rendering (CSR, like a typical React app). Both are full of advantages and disadvantages. But, of course, the conversation is more nuanced. Just because an app is SSR doesn't mean it doesn't do dynamic JavaScript-powered things. And just because an app is CSR doesn't mean it can't leverage any SSR at all. … Read article

Steve Souders, "JavaScript Dominates Browser CPU":

Ten years ago the network was the main bottleneck. Today, the main bottleneck is JavaScript. The amount of JavaScript on pages is growing rapidly (nearly 5x in the last 7 years). In order to keep pages rendering and feeling fast, we need to focus on JavaScript CPU time to reduce blocking the browser main thread.

Alex Russell, describing a prototype of "Never-Slow Mode" in Chrome:

... blocks large scripts, sets budgets for certain

I'm never going to tell you that writing your CSS in CSS (or some syntactic preprocessor) is a bad idea. I think you can be perfectly productive and performant without any tooling at all. But, I also think writing CSS in JavaScript is a good idea for component-based styles in codebases that build all their components with JavaScript anyway.

In this article, Max Stoiber focuses on why to write CSS in JavaScript rather than how to do it. There is … Read article