How to change date format in dhtmlx Gantt?

I have a Gantt template which I downloaded from Gantt Docs

Well, I called my gantt but I want to set the time range to the years 2015-2023, instead of letting it default to days/months, but I don't know where I can change it.

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-type" content="text/html; charset=utf-8">
 <title>Tooltip</title>
</head>
<script src="../../codebase/dhtmlxgantt.js" type="text/javascript" charset="utf-8"></script>
<script src="../../codebase/ext/dhtmlxgantt_tooltip.js" type="text/javascript" charset="utf-8"></script>
<link rel="stylesheet" href="../../codebase/dhtmlxgantt.css" type="text/css" media="screen" title="no title" charset="utf-8">

<script type="text/javascript" src="../common/testdata.js"></script>
<style type="text/css">
    html, body{ height:100%; padding:0px; margin:0px; overflow: hidden;}
</style>
<body>
<div id="gantt_here" style='width:100%; height:100%;'></div>

<script type="text/javascript">

    var tasks =  {
        data:[
            {id:1, text:"Project #2", start_date:"01-04-2013", duration:18,order:10,
                progress:0.4, open: true},
            {id:2, text:"Task #1",    start_date:"02-04-2013", duration:8, order:10,
                progress:0.6, parent:1},
            {id:3, text:"Task #2",    start_date:"11-04-2013", duration:8, order:20,
                progress:0.6, parent:1}
        ],
        links:[
            { id:1, source:1, target:2, type:"1"},
            { id:2, source:2, target:3, type:"0"},
            { id:3, source:3, target:4, type:"0"},
            { id:4, source:2, target:5, type:"2"},
        ]
    };

    gantt.init("gantt_here");
    gantt.parse(tasks);

    gantt.init("gantt_here");
    gantt.parse(demo_tasks);
</script>
</body>
</html>

Solution

Found the solution:

Just changed my gantt settings before calling it

<script type="text/javascript">
gantt.config.scale_unit = "year";
gantt.config.step = 1;
gantt.config.date_scale = "%Y";
gantt.config.min_column_width = 30;
gantt.config.scale_height = 80;

var tasks =  {
    data:[
        {id:1, text:"Project #2", start_date:"01-04-2013", duration:18,order:10,
            progress:0.4, open: true},
        {id:2, text:"Task #1",    start_date:"02-04-2013", duration:8, order:10,
            progress:0.6, parent:1},
        {id:3, text:"Task #2",    start_date:"11-04-2013", duration:8, order:20,
            progress:0.6, parent:1}
    ],
    links:[
        { id:1, source:1, target:2, type:"1"},
        { id:2, source:2, target:3, type:"0"},
        { id:3, source:3, target:4, type:"0"},
        { id:4, source:2, target:5, type:"2"},
    ]
};

gantt.init("gantt_here");
gantt.parse(tasks);

</script>