Before we get going on seeing how to build a SvelteKit PWA let's run it back a little and first
look at what a PWA is. A Progressive Web App (PWA) is an app built to work with HTML, JavaScript and CSS but with the functionality of a native app.
Features include responsiveness and offline availability as well as the possibility to install the
app. You can test a site's PWA capability in Lighthouse .
SvelteKit PWA: Lighthouse screenshot
For all of those mentioned features to work, we need to add some additional super powers to our
SvelteKit app. These include icons of various sizes and a manifest file which contains the app
name, colours and some other properties. As well as those items, we also need to define a service worker to perform background caching and do the groundwork to make the app available offline.
In this post we will look at how to use the PWA functionality in the MDsveX starter blog. After
that we will look at what is under the hood, so you can set up an existing project as a PWA. If
that all matches what you were looking for, why don't we get cracking?
🧱 Create a SvelteKit PWA using the MDsveX Starter #
I have just added PWA functionality to the MDsveX starter . All you need to do is customise the website configuration file with the site's name and theme
colours, then run a script to generate all the different icon sizes automatically. Here is exactly
what you need to do in five simple steps. If you are looking for a more general SvelteKit Tutorial or how to get started with SvelteKit I have a couple of posts you will appreciate.
We are using
the MDsveX starter
. Start by cloning the repo and installing packages. I use pnpm, though if you
prefer npm just swap out pnpm for npm in the commands below:
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After cloning the repo and installing packages, these commands create a `.env` file from the
template provided and fire up the dev server. You can change the server port in `package.json`
if you already have an app running on port 3000 (the default port).
Now you need to customise the configuration file with the details of your app. The website
configuration file is in your project at src/lib/config/website.js. This file
contains data which are used for SEO as well as the parameters needed for our Progressive
Working App. More sensitive data can be pulled from the .env file when needed. Having
said that, for the progressive app customisation, we shouldn't have anything secret. Go ahead
and customise the file (lines 7–11):
In the previous step we set the location for our icon file to static/icon.png.
There is already a dummy file in that location. Replace the dummy file with your own PNG
logo. I recommend you go for a 512 px × 512 px file. All other
needed file sizes will be generated automatically in the next step.
Next we will generate new icon files in all the sizes needed for our PWA. These are
generated using the sharp plugin, which is very efficient. As well as the icons, we will
generate the manifest.json file. Run the command:
pnpm run generate:manifest
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This command triggers a script which is in the file `generate-manifest.js` in the project's root
folder. The script runs automatically before the site is built by default. You might find this
useful while you are still setting up the site and changing a lot of parameters. You can remove
this step in the build process if you want to by changing line `6` of package.json from `npm run generate:manifest && svelte-kit build`
simply to `svelte-kit build`. Anyway you should now have icons and the manifest. Take a look
at `static/manifest` and check the parameters have been updated with your site's parameters.
Here is an example file:
static/manifest.json
json
{
"name":"SvelteKit Blog Mdx",
"short_name":"SvelteKit Blog",
"start_url":"/index.html",
"background_color":"#1b4079",
"theme_color":"#d62828",
"display":"standalone",
"icons":[
{
"src":"icons/icon-128x128.png",
"sizes":"128x128",
"type":"image/png",
"purpose":"any maskable"
},
{
"src":"icons/icon-144x144.png",
"sizes":"144x144",
"type":"image/png",
"purpose":"any maskable"
},
{
"src":"icons/icon-152x152.png",
"sizes":"152x152",
"type":"image/png",
"purpose":"any maskable"
},
{
"src":"icons/icon-192x192.png",
"sizes":"192x192",
"type":"image/png",
"purpose":"any maskable"
},
{
"src":"icons/icon-256x256.png",
"sizes":"256x256",
"type":"image/png",
"purpose":"any maskable"
},
{
"src":"icons/icon-512x512.png",
"sizes":"512x512",
"type":"image/png",
"purpose":"any maskable"
}
]
}
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Next look in `static/icons` you will see your icon in the various pixel sizes.
As ever, we need to check that all of this is working before we deploy. This is easy to do
with Lighthouse in the Chrome Developer Tools. First build the site and generate a preview
site (stop the dev server first if this is running):
pnpm run build
pnpm run preview
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Finally in Chrome Browser, go to localhost:3000. Next go to the View menu and find Developer then click Developer Tools find Lighthouse (you might need to expand the list, it is in the same menu as Elements and
Console). Once you have Lighthouse open click Generate Report. It might
take a couple of minutes to run. You should have big green tick (check mark) under PWA when
the results do show up. Note to get 100 for Best Practices in the latest version of Chrome
you will need to set Content Security Policy to enable mode. By default it is set to report
only mode in the template. It is really easy to switch modes, just edit two lines in src/hooks.js:
src/hooks.js
javascript
85// 'Content-Security-Policy-Report-Only': csp,
86'Content-Security-Policy': csp,
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You just comment out line 85 and uncomment line 86.
SvelteKit PWA: Lighthouse screenshot: PWA check
I hope you find that helpful and see how easy it can be to set up a PWA in SvelteKit. If you are
interested, we will have a quick look under the hood next to see what makes the PWA work.
As mentioned earlier, a script generates the manifest.json file and
icons automatically. There is nothing magic or too special here, but let me know if you would like
some clarification on any aspect. I include the code here in case you want to work something similar
into one of your projects.
There are two elements which you need to add to you page HTML head section on all pages. First is
the theme colour which the browser uses to change the address bar to match your site's colour theme . Finally, there is an icon which iOS uses as the Home Screen icon when the user installs your
app:
This component is included in page layout templates. Because we wrap these elements in a <svelte:head> element, SvelteKit works them in the HTML head section of our page.
Note in line 4 we use the build date in our cache name. This helps
us identify when the cached data is stale. Let me know if you would like more detailed explanations
on anything here. I based this code on Pedro Sonzini Astudillo's Svelte service worker.
how to create a SvelteKit PWA using the MDsveX starter,
what's under the hood in the starter's PWA code.
As always suggestions for improvements, together with requests for explanations and feedback are
more than welcome. Also let me know what other fetaures you would like implemented on the starter.
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