Archive: July 2nd, 2019

Bridgy for Webmentions with Brotli—zachleat.com

This is good to know! Because of a bug in Google App Engine, Brid.gy won’t work for sites using Brotli compression on HTML.

The trimCache function in Going Offline …again

It seems that some code that I wrote in Going Offline is haunted. It’s the trimCache function.

First, there was the issue of a typo. Or maybe it’s more of a brainfart than a typo, but either way, there’s a mistake in the syntax that was published in the book.

Now it turns out that there’s also a problem with my logic.

To recap, this is a function that takes two arguments: the name of a cache, and the maximum number of items that cache should hold.

function trimCache(cacheName, maxItems) {

First, we open up the cache:

caches.open(cacheName)
.then( cache => {

Then, we get the items (keys) in that cache:

cache.keys()
.then(keys => {

Now we compare the number of items (keys.length) to the maximum number of items allowed:

if (keys.length > maxItems) {

If there are too many items, delete the first item in the cache—that should be the oldest item:

cache.delete(keys[0])

And then run the function again:

.then(
    trimCache(cacheName, maxItems)
);

A-ha! See the problem?

Neither did I.

It turns out that, even though I’m using then, the function will be invoked immediately, instead of waiting until the first item has been deleted.

Trys helped me understand what was going on by making a useful analogy. You know when you use setTimeout, you can’t put a function—complete with parentheses—as the first argument?

window.setTimeout(doSomething(someValue), 1000);

In that example, doSomething(someValue) will be invoked immediately—not after 1000 milliseconds. Instead, you need to create an anonymous function like this:

window.setTimeout( function() {
    doSomething(someValue)
}, 1000);

Well, it’s the same in my trimCache function. Instead of this:

cache.delete(keys[0])
.then(
    trimCache(cacheName, maxItems)
);

I need to do this:

cache.delete(keys[0])
.then( function() {
    trimCache(cacheName, maxItems)
});

Or, if you prefer the more modern arrow function syntax:

cache.delete(keys[0])
.then( () => {
    trimCache(cacheName, maxItems)
});

Either way, I have to wrap the recursive function call in an anonymous function.

Here’s a gist with the updated trimCache function.

What’s annoying is that this mistake wasn’t throwing an error. Instead, it was causing a performance problem. I’m using this pattern right here on my own site, and whenever my cache of pages or images gets too big, the trimCaches function would get called …and then wouldn’t stop running.

I’m very glad that—witht the help of Trys at last week’s Homebrew Website Club Brighton—I was finally able to get to the bottom of this. If you’re using the trimCache function in your service worker, please update the code accordingly.

Management regrets the error.

Replying to a tweet from @jaffathecake

Proposal. Yes. That’s accurate.

Replying to a tweet from @jaffathecake

Soooo …maybe don’t call it a web standard?

Design is a (hard) job. | Zeldman on Web & Interaction Design

It me:

Writing comes naturally to me when I’m expressing myself on my own site, with no outside assignment and no deadline except my own sense of urgency about an idea. It’s easy when I’m crafting a brief text message or tweet. Or a letter to a friend.

But give me a writing assignment and a deadline, and I’m stuck. Paralysis, avoidance, a dissatisfaction with myself and the assignment—all the usual hobgoblins spring immediately to life.

Replying to a tweet from @cramforce

It’s not a “web standard” when it’s unilaterrally shipped by one browser vendor prior to any standards discussion.

(I’m not necessarily saying don’t ship it; but calling it a “web standard” is disengenuous, and where the confusion lies.)

Checked in at The Lord Nelson Inn. The Bombadils — with Jessica map

Checked in at The Lord Nelson Inn. The Bombadils — with Jessica