[Error] navigator.serviceWorker.ready + Cannot read property 'ready' of undefined

https://stackoverflow.com/questions/29874068/navigator-serviceworker-is-never-ready

<IfModule mod_headers.c>
    <Files ~ "service-worker\.js">
        Header set Service-Worker-Allowed: /
    </Files>
</IfModule>

Full C:\xampp\htdocs\webpush-example\public.htaccess

<IfModule mod_rewrite.c>
    <IfModule mod_negotiation.c>
        Options -MultiViews -Indexes
    </IfModule>

    RewriteEngine On

    # Handle Authorization Header
    RewriteCond %{HTTP:Authorization} .
    RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]

    # Redirect Trailing Slashes If Not A Folder...
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteCond %{REQUEST_URI} (.+)/$
    RewriteRule ^ %1 [L,R=301]

    # Handle Front Controller...
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteRule ^ index.php [L]
</IfModule>
<IfModule mod_headers.c>
    <Files ~ "service-worker\.js">
        Header set Service-Worker-Allowed: /
    </Files>
</IfModule>