var async = function (div) {
    var board = tnt.board().from(20).to(500).width(950);

    var axis_track = tnt.board.track()
        .height(0)
        .color("white")
        .display(tnt.board.track.feature.axis()
            .orientation("top")
        );

    var pin_track = tnt.board.track()
        .height(60)
        .color("white")
        .display(tnt.board.track.feature.pin()
            .domain([0.3, 1.2])
            .color("red")
        )
        .data(tnt.board.track.data.async()
            .retriever (function () {
                var track = this;
                var arr = [
                    {
                        pos : 200,
                        val : 0.5
                    },
                    {
                        pos : 355,
                        val : 0.8
                    },
                    {
                        pos : 100,
                        val : 0.3
                    },
                    {
                        pos : 400,
                        val : 1
                    },
                    {
                        pos : 401,
                        val : 1
                    }
                ];

                return new Promise (function (resolve, reject) {
                    // We "fake" async data by delaying 1s
                    setTimeout(function () {
                        resolve(joinClose(arr, track.display().scale()));
                    }, 1000);
                });
            })
         );

    board
        .add_track(axis_track)
        .add_track(pin_track);

    board(div);
    board.start();
};

function joinClose (arr, xScale) {
    var lim = 2;
    arr.map (function (d) {
        d._px = xScale(d.pos);
    });
    arr.sort (function (a, b) {
        return a.pos > b.pos;
    });
    var groups = [];
    var currGroup = [arr[0]];
    var curr = arr[0];
    for (var i=1; i<arr.length; i++) {
        if ((arr[i]._px - curr. _px) < lim) {
            currGroup.push(arr[i]);
        } else {
            groups.push (currGroup);
            currGroup = [arr[i]];
            curr = arr[i];
        }
    }
    groups.push (currGroup);
    for (var g=0; g<groups.length; g++) {
        if (groups[g].length > 1) {
            var med = groups[g][~~(groups[g].length / 2)];
            med.label = groups[g].length;
        }
    }
    return arr;
}