.htaccess remove trailing slash - .htaccess

Question

I have a htaccess file for a site to let it's script work . I don't know much about how it works, but I have to remove the trailing slash at the end.
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ index.php?/$1 [L]
RewriteCond %{HTTPS} off
RewriteRule .* https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
RewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteRule .* https://www.%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
ErrorDocument 404 https://www.onlinegames.nl/
## 301 Redirects
# 301 Redirect 1
RewriteCond %{HTTP_HOST} ^www\.onlinegames\.nl$ [NC]
RewriteCond %{QUERY_STRING} ^$
RewriteCond %{HTTPS} =on
RewriteRule ^index\.html$ https://www.onlinegames.nl/? [R=301,NE,NC,L]
<IfModule mod_headers.c>
<FilesMatch "\.(ttf|ttc|otf|eot|woff|woff2|font.css|css|js)$">
Header set Access-Control-Allow-Origin "*"
</FilesMatch>
</IfModule>
How can I remove the trailing slash at the end? I've tried to change a few things, but most of the times the script is not working correctly anymore and all the subpages are not working anymore.

Answer 1

You may use these rules in your site root .htaccess to replace your shown code. Note that ordering of these rules is also important and change in ErrorDocument.
ErrorDocument 404 /
RewriteEngine On
# remove www from host names
RewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteRule ^ https://www.%{HTTP_HOST}%{REQUEST_URI} [R=301,L,NE]
# redirect http to https
RewriteCond %{HTTPS} off
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301,NE]
# Unless directory, remove trailing slash
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} ^(.+)/+$
RewriteRule ^ %1 [R=301,NE,L]
# strip /index.html
RewriteCond %{QUERY_STRING} ^$
RewriteRule ^index\.html$ / [R=301,NC,L]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ index.php?/$1 [L]