You can get ISP information by using node-whois module but in its response it quite complex to access value for a particular key. So there is another way is you can use satellite module, This module can give quick response and response is available in json format so you can access any key values easily. Here is the code.
var satelize = require('satelize');
var ExternalIP = "173.194.70.100"; // I asume that, you already have external(public)IP
satelize.satelize({ip: ExtenalIP}, function(err, geoData)
{
if(err){
console.log(" Error in retriving ISP Information");
}
else
{
console.log("ISP Information for "+ ExternalIP+" :"+geoData );
}
});