[javascript] Get client IP address via third party web service

If you face an issue of CORS, you can use https://api.ipify.org/.

function httpGet(theUrl)
{
    var xmlHttp = new XMLHttpRequest();
    xmlHttp.open( "GET", theUrl, false );
    xmlHttp.send( null );
    return xmlHttp.responseText;
}


publicIp = httpGet("https://api.ipify.org/");
alert("Public IP: " + publicIp);

I agree that using synchronous HTTP call is not good idea. You can use async ajax call then.