native javaScript ES6. just insert this file in any HTML and js will do rest of work.

synacor_weather.js

let XHR = (`onload` in new XMLHttpRequest()) ? XMLHttpRequest : XDomainRequest; //to support IE8
let ipXhr = new XHR(),
    weatherXhr = new XHR();

let creatElement = function () {
    let layoutBody = document.createElement('div'),
        h1 = document.createElement('h1'),
        p = document.createElement('p'),
        img = document.createElement('img'),
        h2 = document.createElement('h2');

    layoutBody.id = "layout__body";
    h1.id = "city";
    p.id = "temp";
    img.id = "icon";
    h2.id = "description";

    layoutBody.appendChild(h1);
    layoutBody.appendChild(p);
    layoutBody.appendChild(img);
    layoutBody.appendChild(h2);
    document.body.appendChild(layoutBody);
}();

ipXhr.open(`GET`, `https://weathersync.herokuapp.com/ip`, true);
ipXhr.send();

ipXhr.onreadystatechange = function () {
    let lat = ``,
        lng = ``;

    if (ipXhr.readyState != 4) return;
    if (ipXhr.status != 200) {
        console.log(`error ${ipXhr.status}: ${ipXhr.statusText}`);
    } else {
        let ip = JSON.parse(ipXhr.responseText);
        lat = ip.location.latitude;
        lng = ip.location.longitude;

        weatherXhr.open(`GET`, `https://weathersync.herokuapp.com/weather/${lat},${lng}`, true);
        weatherXhr.send();
        weatherXhr.onreadystatechange = function () {
            if (weatherXhr.readyState != 4) return;
            if (weatherXhr.status != 200) {
                console.log(`error ${weatherXhr.status}: ${weatherXhr.statusText}`);
            } else {
                let obj = JSON.parse(weatherXhr.responseText),
                    city = obj.name,
                    temp = Math.floor(1.8 * (obj.main.temp - 273) + 32), //Convert Kelvin to Fahrenheit
                    icon = `http://openweathermap.org/img/w/${obj.weather[0].icon}.png`,
                    description = obj.weather[0].description;

                document.getElementById(`city`).innerHTML = city;
                document.getElementById(`temp`).innerHTML = `${temp} ºF`;
                document.getElementById(`icon`).src = icon;
                document.getElementById(`description`).innerHTML = description;
            }
        }
    }
};