getIP.js

/**
 * Get current user IP (in callback)
 * @param {string} callback 
 */
function getIp(callback){
    var url = 'https://api.ipify.org/';
    var xhr = new XMLHttpRequest();
    xhr.onreadystatechange = function(){
        if(this.readyState === XMLHttpRequest.DONE)
            if(this.status === 200)
                callback.apply(this.responseText);
    }
    xhr.open('GET', url, true);
    xhr.send();
}