Populating a dropdown list with an ajax request.

DropdownLoader.js

function DropdownLoader(options) {
    var options = options,
        loading = false,
        completed = false;
    var obj = document.querySelector(options.selector);

    function load() {
        loading = true;
        var xml = new XMLHttpRequest();
        xml.open("GET", options.url, true);
        options.loading();
        xml.onload = function() {
            // Loading işleminin bittiğini söylüyoruz.
            loading = false;
            // Ajax cevabını parseleyip, sonuç var ise dropdown'a ekle
            result = options.parser(this.responseText);
            if (result != false) {
                completed = true;
                obj.innerHTML = result;
            } else {
                completed = !!!options.retry;
                if (options.retry) load();
            }
            options.finished(result != false ? null : -1);
        };
        // Veri yüklemede hata olursa çalışacak olan fonksiyonu belirtiyoruz.
        xml.onerror = function() {
            loading = false;
            options.finished(this);
        };
        xml.send();
    }

    obj.addEventListener("click", function() {
        if (loading || completed) return false;
        load();
    });
}

index.html

<select id="combobox">
    <option disabled selected></option>
    <option>Loading...</option>
</select>

Scripts.js

new DropdownLoader({
    selector: "#combobox",
    url: "http://api.openweathermap.org/data/2.5/box/city?bbox=12,32,15,37,10&cluster=yes&appid=2de143494c0b295cca9337e1e96b00e0",
    parser: function(response) {
        var weather_data = JSON.parse(response),
            result = "";

        for (var key in weather_data["list"]) {
            var data = weather_data["list"][key];

            result += "<option>" + data["name"] + '-' + data["weather"]["0"]["main"] + "</option>"
        }
        return result;
    },
    loading: function() {
        console.log("Loading...");
        if (this.times == undefined) this.times = 0;
        if (++this.times == 5) {
            this.retry = false;
            console.log("No more retries...");
        }
    },
    finished: function(err) {
        console.log("Finished: ", err);
    },
    retry: true
});