var xhr = new XMLHttpRequest();
xhr.open("GET", "https://api.netatmo.com/api/getpublicdata?access_token=YOUR_ACCESS_TOKEN&lat_ne=48.8588443&lon_ne=2.2943506&lat_sw=48.8588443&lon_sw=2.2943506", true);
xhr.onreadystatechange = function() {
    if (xhr.readyState === 4 && xhr.status === 200) {
        var json = JSON.parse(xhr.responseText);
        var temperature = json.body.temperature;
        document.getElementById("weather").innerHTML = temperature + "°C";
    }
};
xhr.send();