Snippets

On the surface, Service Workers look quite similar to Web Workers. They both run on separate threads from the main UI thread, they have a global self object, and they tend to support the same APIs. However, while Web Workers offer a large degree of control over their lifecycle (you can create and terminate them at will) and are able to execute long-running JavaScript tasks (in fact, they’re designed for this), Service Workers explicitly don’t allow either of these things. In fact, a Service Worker is best thought of as “fire-and-forget” — it responds to events in an ephemeral way, and the browser is free to terminate any Service Worker that takes too long to fulfill a request or makes too much use of shared resources.

This led us to our first real hurdle with Service Worker. Our goal, as we originally conceived it, was to use PouchDB’s existing replication APIs to enable bi-directional sync between the client and the server, with the client code isolated entirely to the Service Worker.

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This resulted in a silent error, which took quite a while to debug. The culprit? Well, PouchDB’s “live” sync depends on HTTP longpolling — in other words, it maintains an ongoing HTTP connection with the CouchDB server, which is used to send real-time updates from the server to the client. As it turns out, this is a big no-no in Service Worker Land, and the browser will unceremoniously drop your Service Worker if it tries to maintain any ongoing HTTP connections. The same applies to Web Sockets, Server-Sent Events, WebRTC, and any other network APIs where you may be tempted to keep a constant connection with your server.

What we realized is that “the Zen of Service Worker” is all about embracing events. The Service Worker receives events, it responds to events, and it (ideally) does so in a timely manner — if not, the browser may preemptively terminate it. And this is actually a good design decision in the spec, since it prevents malicious websites from installing rogue Service Workers that abuse the user’s battery, memory, or CPU.

For years, base or reset stylesheets have helped web developers get started faster.

Early resets eliminated all visual styling, putting the burden of defining styles for every element on the webmaster. This made sense when there weren’t as many elements or properties, and when each browser did something very different than the others. By zeroing everything out, you start from a blank page. There were many reset stylesheets that took this approach. Eric Meyer’s became the most popular.

More recently, Normalize and similar projects took a different approach. Rather than removing all styling, they set out to create sensible defaults and eliminate browser bugs. Use one of these and you get a consistent base across all browsers.

CSS Remedy takes a slightly different approach. These days, browsers are far more consistent in how they render CSS. But there are limitations on how far browsers can improve their User Agent Stylesheet. The defaults for the web have to be consistent with the past. Many desirable changes would break millions of existing websites.

You, however, don’t have to stay in the past. You can override the UA styles with more modern ideas of how CSS should work by default. Introducing CSS Remedy.

FLIP is an approach to animations that remaps animating expensive properties, like width, height, left and top to significantly cheaper changes using transforms. It does this by taking two snapshots, one of the element’s First position (F), another of its Last position (L). It then uses a transform to Invert (I) the element’s changes, such that the element appears to still be in the First position. Lastly it Plays (P) the animation forward by removing the transformations applied in the Invert step.

By default, backgrounds cover the entire border-box (they are applied underneath the border as well), but their background-position (and also %-based background-size) is relative to the padding-box.

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We can make the background cover just the padding-box or just the content-box with the help of background-clip.

clip-path is one of those CSS properties we generally know is there but might not reach for often for whatever reason. It’s a little intimidating in the sense that it feels like math class because it requires working with geometric shapes, each with different values that draw certain shapes in certain ways.

We’re going to dive right into clip-path in this article, specifically looking at how we can use it to create pretty complex animations. I hope you’ll see just how awesome the property and it’s shape-shifting powers can be.

Favicons are actually at their most useful when you’re not active on a tab. Here’s an example:

Imagine you’re backing up photos from your recent summer vacation to a cloud service. While they are uploading, you’ve opened a new tab to gather details about the places you went on vacation to later annotate those photos. One thing led to the other, and now you’re watching Casey Neistat on the seventh tab. But you can’t continue your YouTube marathon without the anxious intervals of checking back on the cloud service page to see if the photos have been uploaded.

It’s this type of situation where we can get creative! What if we could dynamically change the pixels in that favicon and display the upload progress? That’s exactly what we’ll do in this article.

In supported browsers, we can display a loading/progress animation as a favicon with the help of JavaScript, HTML <canvas> and some centuries-old geometry.

While the article primarily deals with a square favicon, the author also provides code for a circular favicon as well.