Use a callback() function inside the foo() success. Try in this way. It is simple and easy to understand.   

var lat = "";
var lon = "";
function callback(data) {
    lat = data.lat;
    lon = data.lon;
}
function getLoc() {
    var url = "http://ip-api.com/json"
    $.getJSON(url, function(data) {
        callback(data);
    });
}

getLoc();

Use a callback() function inside the foo() success. Try it in this way. It is simple and easy to understand.

var lat = "";
var lon = ""; 

function callback(data) {
    lat = data.lat;
    lon = data.lon;
} 

function getLoc() {
    var url = "http://ip-api.com/json"
    $.getJSON(url, function(data) {
        callback(data);
    });
}

getLoc();

Use a callback() function inside the foo() success. Try in this way. It is simple and easy to understand.

var lat = "";
var lon = "";
function callback(data){
    lat = data.lat;
    lon = data.lon;
}
function getLoc() {
  var url = "http://ip-api.com/json"
  $.getJSON(url, function(data) {
    callback(data);
  });
}

getLoc();

Use a callback() function inside the foo() success. Try in this way. It is simple and easy to understand.   

var lat = "";
var lon = "";
function callback(data) {
    lat = data.lat;
    lon = data.lon;
}
function getLoc() {
    var url = "http://ip-api.com/json"
    $.getJSON(url, function(data) {
        callback(data);
    });
}

getLoc();