In an effort to promote my upcoming book, I created the website https://sveltekitbook.dev. It has all of the information one may want to know before purchasing a copy. Of course, the book is about #SvelteKit so I had to build the site using #SvelteKit. I decided to take the opportunity to learn the latest technology web developers can’t shut up about; #TailwindCSS.
In my last post, I prefaced it by saying that I haven’t been posting here often because I’ve been busy. In reality, I only missed a single post back in May so I guess you could say that I haven’t actually quit writing.
(But you’ve already clicked the link and are reading the post so the bait worked, right? Might as well stick around for the rest.) 😎
In fact, I’ve doubled down on the writing because the latest project that has been keeping me so incredibly busy has been…
…writing my first book!
SvelteKit Up and Running
That’s right! An entire book made out of paper and ink like they used to have back in the ye olden days. Of course, there will be digital copies for you technology enthusiasts as well. The book is titled SvelteKit Up and Running: Building High Performance Web Apps with a Next Generation Framework. It is obviously about SvelteKit, the highly performant web application meta framework from the creators of Svelte. I wrote it because I wanted to give others the resource I wish I had when I was learning how to build web apps with Svelte and SvelteKit.
Whether you’re new to JavaScript development and are wondering which framework to pick up first, or are a seasoned developer tired of the bloat that comes with other popular frameworks; this book will teach you the concepts behind the project leading the field in revolutionizing JavaScript development. The examples found throughout the book are concise, practical, and easy to follow along with while still effectively demonstrating how to leverage the various techniques necessary for implementing features commonly found in web applications.
Pre-order
As of this writing, the book is currently trending #3 on Amazon! How wild is that?
If you’re interested in getting a copy (and I hope you are), it’s available for pre-order now at https://packt.link/bVAyJ! The book is scheduled for release on July 28th, 2023.
Want more?
If you’re curious about what it takes to write a book, the process behind it, how I got started, and lessons I learned, then be sure to subscribe to this site’s RSS feed, follow me on Telegram, or find me in the Fediverse. I’ll be posting more updates as well as outlining my experience throughout the entirety of this project!
On this website, I normally only write about solutions I’ve come up with to problems I’ve encountered (pertaining to web development). I recognize that’s not entirely authentic because I can’t solve every problem I come across. Sometimes, I’ll come across an issue where the solution isn’t immediately clear to me. Sometimes, it festers for long enough that I’m driven to take drastic action. Sometimes, I’m forced to write an entire post about it. This is post about one of those festering, unsolved problems.
It started while working on the Svelte Work:Rest Timer component I wrote about a few months ago. You see, the timer was intended to be a static Single Page Application (SPA)/Progressive Web Application (PWA) without a back-end server component. That is, once served to the client and installed via the browser PWA installation process, it would be usable on mobile devices whether or not they had an internet connection. I thought surely, this will be easy enough for me to tackle since I’ve already built something similar with helth app. The only major difference being that this timer application would utilize the SvelteKit static site adapter instead of the Node.js adapter.
The Problem
During development, everything ran smoothly. It wasn’t until deployment to production that I noticed issues.
SvelteKit uses Vite to deliver that buttery-smooth development experience, and Vite uses esbuild to bundle an application during development. However, when building the production version of an application, Vite uses Rollup to bundle the app. I believe this discrepancy; coupled with my obvious lack of understanding of the underlying technologies behind SvelteKit (Vite, esbuild, and Rollup), is why I ran into any issues in the first place.
When I attempted to deploy my static files to a static host, I noticed the app was missing several key features, like some of the actual code that made the logic in the application run and the CSS included in each component. After checking the network requests in my developer console, I noticed the development version was making 3-5 more requests than my production build. Why?
When deployed, the production build was very broken.
Troubleshooting
Since I had built the application to be static, it was safe to prerender the HTML on the one and only page. Any two users should see identical HTML, CSS, and JS on the site when they open it for the first time. To accomplish this, I simply needed to add the following code to the file src/routes/+layout.js:
export const prerender = true;
export const ssr = false;
I figured since there wouldn’t be a back-end component of the application, it would be fine to disable Server-Side Rendering (SSR) while I was at it. My thought was that this would force SvelteKit to prerender and it would skip generating any server-side code for that route.
I discovered that if I removed the line that disabled SSR, I would get a different index.html located at .svelte-kit/output/prerendered/pages/index.html.
Left: index.html included in “build/”Right: index.html included in “.sveltekit-output/prerendered/pages/” when option that disables SSR is removed
This file contained links to resources that were not being loaded in my production version of the app. This file was also not included in my production build folder (build/). I don’t fully understand why disabling SSR and enabling prerendering generates a different version of the index.html file. I also don’t understand why the version of index.html I needed wasn’t included in my build directory. For now, I’ve simply overwritten the file build/index.html with the file .svelte-kit/output/prerendered/pages/index.html and the application works as expected.
If you or someone you know has some insight as to why this is, please drop a comment below, reach out to me via my contact form, or message me on various social media platforms. I would love to understand what I assume I’m doing wrong.
I was recently approached by a friend to build an app. Now, I’ve been cornered and pitched far too many half-brained apps in my day but it is refreshing to hear a good pitch. This pitch was for a timer, but not just any timer or stopwatch app that comes preinstalled on your phone. Rather, it was a workout timer that would also time your rests. As someone who often takes too long to rest between sets, I thought this sounded like a decent idea. I was told “nothing like this exists!” but a quick search of the web proves that false; it’s definitely been done. But I could do it as a Svelte component! And it’d be a fun coding challenge!
The Setup
If you’ve read any recent posts of mine, you know I’ve been working with SvelteKit lately. To get started with SvelteKit, I ran a few commands in the project directory:
npm create svelte@latest timer
cd timer
npm install
npm run dev
From there, I created the file /src/routes/+page.svelte as the entry point page for the app. I also created the file /src/lib/timer.svelte which is where all of the magic happens and included it in the aforementioned +page.svelte like so:
+page.svelte
<script>
import Timer from ‘$lib/timer.svelte’;
</script>
<div class=’content’>
<Timer />
</div>
<style>
div.content {
text-align: center;
width: 100%;
background-color: #130d0d;
position: absolute;
top: 0;
left: 0;
right: 0;
bottom: 0;
color: #d9d9d7;
}
</style>
$lib is an alias to /src/lib/ that is supported by SvelteKit out of the box.
The Markup
Most timers have a display of the running time, a start button, a stop button, and reset button so I went ahead and included those right away in /src/lib/timer.svelte. I also gave it some rough styling so it wasn’t awful to look at while testing. The basic structure of the component looks something like this:
<script>…</script>
<h1>Work+Rest Timer</h1>
<div class=’time’>{hr}:{min}:{s}.{ms}</div>
<div class=’controls’>
<button class=’start’ on:click={start}>{running ? `rest` : `start`}</button>
<button class=’stop’ on:click={stop}>stop</button>
<button class=’reset’ on:click={reset}>reset</button>
</div>
<style>
h1 {
text-align: center;
}
.time {
margin: 1.5rem;
font-size: 4rem;
}
.controls {
display: grid;
grid-template-columns: 1fr 1fr 1fr 1fr;
grid-template-rows: 1fr 1fr;
}
button {
padding: 1.1rem 1.4rem;
margin: 1.1rem;
font-size: 1.5rem;
border: none;
background-color: #496bf0;
color: white;
transition: all .4s ease-in-out;
cursor: pointer;
grid-column: 3 / 4;
grid-row: 2 / 3;
}
button:hover {
background-color: #2047df;
}
button.stop {
background-color: #df3d2c;
grid-column: 2 / 3;
grid-row: 2 / 3;
}
button.stop:hover {
background-color: #a81303;
}
button.start {
background-color: #408e2a;
grid-column: 2 / 4;
grid-row: 1 / 2;
}
button.start:hover {
background-color: #245e14;
}
</style>
Yup, that’s a timer alright.
Eagle eyed readers likely noticed that there are some variables used in the markup that were not declared in the script tag. Lets get to that part now.
The Logic
This timer needs to be able to start, stop, reset, and display the running time. It also needs a “rest” feature which counts down to zero from whenever the “rest” button was clicked. To prevent users from starting another timer, I decided to turn the start button into the rest button while the timer is running. A quick rundown of how this ought to work:
clicking “start” starts the timer (duh)
the time since start is displayed in hours, minutes, seconds, and milliseconds
after clicking “start,” the “start” button becomes the “rest” button
clicking the “rest” button will reverse the time, counting down to zero
when the timer reaches zero, it will start counting up again until stopped or until “rest” is clicked again
clicking “stop” will stop the time
clicking reset will set hours, minutes, seconds, and milliseconds back to zero
That all seems fairly straightforward, right? Oh, but dear reader, you don’t know this (how could you have?) but when it comes to code, I hate programming anything related to time. And I’m really bad at math.
So why did I think this was a good idea? 🤔 Who knows? Maybe I just hate myself.
Side note: When working with computers and time, there’s all sorts of problems that can arise. It’s a lot easier to do math with time when you convert time to a regular number.
About those missing variables…
<script>
let interval = null;
let running = false;
let elapsed = 0;
let oldElapsed = 0;
$: ms = pad3(0);
$: s = pad2(0);
$: min = pad2(0);
$: hr = pad2(0);
// pad2/3 exist to format the numbers with leading zeros
const pad2 = (number) => `00${number}`.slice(-2);
const pad3 = (number) => `000${number}`.slice(-3);
const start = () => {
…
}
const stop = () => {
…
}
const reset = () => {
…
}
</script>
You’ll notice some that weren’t mentioned the markup; you can ignore those for now. The times (hr, min, s, ms) are all declared as reactive because I want the timer display to update as the those values change. Now all of this keeps the component from throwing errors but it doesn’t do anything. To make it do the things, let’s look at start() first.
const start = () => {
if(!running) {
countUp();
}
else {
countDown();
}
}
There! That was easy. Lets move on to the stop() and reset() functions:
const stop = () => {
clearInterval(interval);
oldElapsed = elapsed;
}
const reset = () => {
s = min = hr = pad2(0);
ms = pad3(0);
elapsed = oldElapsed = 0;
running = false;
clearInterval(interval);
}
Wait a minute, this doesn’t make any sense without looking at what’s actually going on in start(). Let’s back up. Here’s countUp() which is called by start() when running is false.
const countUp = () => {
let startTime = Date.now();
running = true;
interval = setInterval(() => {
elapsed = Date.now() – startTime + oldElapsed;
ms = pad3(elapsed);
s = pad2(Math.floor(elapsed / 1000) % 60);
min = pad2(Math.floor(elapsed / 60000) % 60);
hr = pad2(Math.floor(elapsed / 3600000) % 60);
});
}
The secret sauce here is setInterval(). Since it has not been provided the optional second argument, it loops on the function passed to it every millisecond. In that loop, the time since the counter began counting upwards is calculated by subtracting the start time from the current time. Then, each “section” of the timer display is calculated based on that elapsed time (and padded with extra leading zeros). Since the interval is assigned to the variable interval, I can clear it later on in stop() and reset() to stop the code.
Now for the part that I spent way too long on; countDown().
const countDown = () => {
stop();
const end = Date.now() + elapsed;
interval = setInterval(() => {
elapsed = end – Date.now();
ms = pad3(elapsed);
s = pad2(Math.floor(elapsed / 1000) % 60);
min = pad2(Math.floor(elapsed / 60000) % 60);
hr = pad2(Math.floor(elapsed / 3600000) % 60);
if(elapsed <= 0) {
clearInterval(interval);
reset();
countUp();
}
});
}
The first thing I want to do here is stop the timer where it’s at. That way, I can clear the value inside the interval variable. Once that’s done, the end time of the new timer needs to be calculated. That’s done by taking the amount of time elapsed and adding it to the current time. Once the end time has been calculated, the loop that runs every millisecond begins, where the amount of time elapsed is recalculated by subtracting the current time from the end time. It is then all shown in the timer display, and when the amount of elapsed time reaches zero, the interval is cleared, values are all reset to zero, and the count back up begins again.
If you were confused during any of that, that’s fine. You’re probably a sane, well adjusted human being that gets along perfectly well in social interactions. Congratulations 🥳!
All Together Now!
<script>
let interval = null;
let running = false;
let elapsed = 0;
let oldElapsed = 0;
$: ms = pad3(0);
$: s = pad2(0);
$: min = pad2(0);
$: hr = pad2(0);
const pad2 = (number) => `00${number}`.slice(-2);
const pad3 = (number) => `000${number}`.slice(-3);
const countUp = () => {
let startTime = Date.now();
running = true;
interval = setInterval(() => {
elapsed = Date.now() – startTime + oldElapsed;
ms = pad3(elapsed);
s = pad2(Math.floor(elapsed / 1000) % 60);
min = pad2(Math.floor(elapsed / 60000) % 60);
hr = pad2(Math.floor(elapsed / 3600000) % 24);
});
}
const countDown = () => {
stop();
const end = Date.now() + elapsed;
interval = setInterval(() => {
elapsed = end – Date.now();
ms = pad3(elapsed);
s = pad2(Math.floor(elapsed / 1000) % 60);
min = pad2(Math.floor(elapsed / 60000) % 60);
hr = pad2(Math.floor(elapsed / 3600000) % 24);
if(elapsed <= 0) {
clearInterval(interval);
reset();
countUp();
}
});
}
const start = () => {
if(!running) {
countUp();
}
else {
countDown();
}
}
const stop = () => {
clearInterval(interval);
oldElapsed = elapsed;
}
const reset = () => {
s = min = hr = pad2(0);
ms = pad3(0);
elapsed = oldElapsed = 0;
running = false;
clearInterval(interval);
}
</script>
I put together a repository of this code so you can read it in all of its glory there. If you follow the development, you’ll see new features like “beeps”, fun colors, and buttons that allow you to multiply the rest time by a factor of 1.5, 2, or even 3! If you like tracking calories as well as working out, then keep a watchful eye out for this new feature coming to your favorite health tracking application.