Nginx run javascript when url is opened by a user

Question

Is it somehow possible to run a javascipt code from Nginx in the web page when a particular url is opened from a browser by a user? For example when user opens https://example.net/test/page , javascript is executed in that web page.

Current Nginx settings:

server {
    listen 443 ssl;
    server_name example.net;

    access_log      /var/log/nginx/example.net.ssl.access.log;
    error_log       /var/log/nginx/example.net.ssl.error.log;

    ssl_certificate         /etc/letsencrypt/live/example.net/cert.pem;
    ssl_certificate_key     /etc/letsencrypt/live/example.net/privkey.pem;

    location / {
        proxy_set_header X-Forwarded-Host $host;
        proxy_set_header X-Forwarded-Server $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_pass http://localhost:8080;
    }
}

How can I edit these settings in order to call a javascript from the "/path/to/file.js" to execute it only when user opens https://example.net/test/page ? In other pages script should't be executed. I would really appreciate any advice. Thank you!

Answer 1

You can try to use nginx SubFilter module to append a script to the document returned from the upstream. For example, you can replace the </head> tag with the <script src="/path/to/script.js"></script></head> string:

map $uri $script {
    # only when URI is '/test/page'
    /test/page  '<script src="/path/to/script.js"></script>';
    # default value will be an empty string
}

server {
    ...
    location / {
        proxy_set_header X-Forwarded-Host $host;
        proxy_set_header X-Forwarded-Server $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_pass http://localhost:8080;
        sub_filter '</head>' '$script</head>';
    }
    # only one special location to serve locally
    location = /path/to/script.js {
        alias /full/path/to/script.js;
    }
}