Question

I want to create a JSON array like this:

var ddBasic = [
    { text: "Facebook", value: 1, },
    { text: "Twitter", value: 2, },
    { text: "LinkedIn", value: 3, },
    { text: "Foursquare", value: 4, }
];

I’m using data from last.fm, so it would be something like this:

var tags = [
        { text: "rock", value: "rock", },
        { text: "pop", value: "pop", },
    ];

It needs to have a comma at the end so the ddslick dropdown function ignores the imageSrc and other things it can use for a dropdown, other it throws this error:

Uncaught TypeError: Cannot read property 'imageSrc' of undefined

To tie everything together, I have:

$('#tag').ddslick({
    data: tags,
    onSelected: function(selectedData) {}   
});

This is the function that gets the tags:

var tags = [];

var getTopTracks = function () {
    $.getJSON(
    settings.PHP_REQUEST_URL, {
        method: "tag.getTopTags",
        api_key: settings.LASTFM_APIKEY,
        format: "json",
    },

    function (data) {
        var limit = 50;

        data.toptags.tag.sort(function (t1, t2) {
            return t2.count - t1.count;
        });

        $.each(data.toptags.tag, function (i, item) {
            if (i > limit) return false;
            console.log(item.name);
            tags.push({
                text: item.name,
                value: item.name
            });
        });
    });
};

// event handlers (load quando o form é invocado só)
getTopTracks();
alert(tags.length);

// define tema para a combobox   
$('#tag').ddslick({
    data: tags,
    onSelected: function (selectedData) {}
});

How can I accomplish this?

Answer 1

var tags = []; //initialised tags with length 0
getTopTracks(); //fetching date in background (!)
alert(tags.length); //running while data is still fitched (unless you've a 0ping connection => alerting length 0

At the point you use the alert it’s very likely tags is not filled as $.getJSON() is an asynchronus request, meaning the request will be handled in the background and execution of the script continues. You have to use the callback method as you already did for filling up the array.

This, getJSON, is a shorthand Ajax function, which is equivalent to:
$.ajax({   
   url: url,
   dataType: 'json',
   data: data,
   success: callback
});

http://api.jquery.com/jQuery.getJSON/

//getJSON success callback:
function (data) {
    var limit = 50;

    data.toptags.tag.sort(function (t1, t2) {
        return t2.count - t1.count;
    });

    $.each(data.toptags.tag, function (i, item) {
        if (i > limit) return false;
        console.log(item.name);
        tags.push({
            text: item.name,
            value: item.name
        });
    });
    //alert the length AFTER the tags been pushed
    alert(tags.length);

    // define tema para a combobox   
    $('#tag').ddslick({
        data: tags,
        onSelected: function (selectedData) {}
    });
}