I've got a config file like:

http {
proxy_cache_path /var/www/nginx/cache levels=1:2 keys_zone=tmpcache:100m;

server {
location ~ \.js$ {
proxy_cache tmpcache;
proxy_cache_key $uri$is_args$args;
proxy_pass http://global;
}
}
}

However, I'm not seeing any data stored in the tmpcache. No folders created, no files. What am I missing?