404 not implemented

[tempral]

if I try to visit a not existent page (or router destination), the div content just display the value "undefined"

[tempral]

would be better to set up an apache config with an .htacces in the homepage folder?

RewriteEngine On
RewriteCond %{HTTPS} off [OR]
RewriteCond %{HTTP_HOST} ^www. [NC]
RewriteCond %{HTTP_HOST} ^(?:www.)?(.+)$ [NC]
RewriteRule ^ https://%1%{REQUEST_URI} [L,NE,R=301]
RewriteCond %{REQUEST_FILENAME} -s [OR]
RewriteCond %{REQUEST_FILENAME} -l [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^.$ - [NC,L]
RewriteRule ^(.) /index.html [NC,L]

[tempral]

I guess that in the github pages hosting there is no possibilities to use the .htaccess,
but is possible in the most common and simplest hosting plans

[tempral]

because your workaround of using a dynamic redirect from the 404 isn't a best practise solution, especially for search engine optimization