add_extension

This command allows you to inject an external script code from the specified file into the current page.

{
    "name": "add_extension",
    "args": [
        "/www/web/script_extensions/extension.js"
    ]
}

If the script was properly injected the response should be:

{
    "response": "success"
}

For more details on how this works check PhantomJS injectJS documentation