You could format the dates before you add them to your array. That is how I did. I used AngularJS
//convert the date to a standard format
var dt = new Date(date);
//take only the date and month and push them to your label array
$rootScope.charts.mainChart.labels.push(dt.getDate() + "-" + (dt.getMonth() + 1));
Use this array in your chart presentation