There are a few things you need to do to get the Svelte default app to run over HTTPS on localhost.

First, generate a certificate and key. Save these as certificate.crt and certificate.key in the project’s folder.

Next, edit package.json. Change the “start” command to:

"start": "sirv public --no-clear --single --http2 --port 5000 --cert certificate.crt --key certificate.key"

Note that port 5000 is the default, so technically --port 5000 is redundant, but if you were to change it, this is where you would change it. When you run npm run dev, the application will now run on https://localhost:5000. Note, though, that livereload.js will still be running as http and will fail. Here’s how we fix that.

Edit rollup.config.js. Import the node fs command we need (Note: this is a node library so you don’t need any new imports in package.json):

import { readFileSync } from 'fs'

Replace the line:

 !production && livereload('public'),

With:

 !production && livereload({
    watch: 'public',
    port: 5001,
    https: {
        key:  readFileSync( 'certificate.key'),
        cert: readFileSync('certificate.crt'),
    },
}),

Here I’ve set the port to 5001, but if omitted it will default to some other port.