AmCharts v4 linechart, starts dateaxis 1 month late

Question

Using amcharts 4 i am displaying an xy chart (simple line graph). Each datapoint has the data set in chart.data, the first as and the following with 1 week intervals:

{
   "Date": new Date(2015, 12, 31), 
   "Value: 12345,
   "LineColor: "#000000"
}, {
   "Date": new Date(2016, 01, 07), 
   "Value: 234567,
   "LineColor: "#000000"
}

Despite this, the first dateAxis point displayed on the chart is (after formatting) Sun 31 Jan 2016, which is not among the dates input.

If i change the dateAxis.baseInterval to timeUnit: "week", count: 1 I get 28 jan 2016, which is amongst the input dates, but the 5th from the top.

I have been searching for something similar to this problem, but it does not seem like this is a commonly experienced problem. Am I missing out on some piece of code that forces the dateaxis to actually use the date input?

Sorry for the lack of code example, if needed i can include more, but currently it's on a secluded machine.

Answer 1

Note that your first date is not December. Months in the JavaScript Date API go from 0-11, which explains why it gets set to January instead and the second date is in Feburary.

If you want more granularity in your axis, set the baseInterval to a day instead of a week/seven days:

dateAxis.baseInterval = {
  "timeUnit": "day",
  "count": 1
};

If you only want to show labels from your data, set skipEmptyPeriods to true as well.

dateAxis.skipEmptyPeriods = true;

Demo below:

var chart = am4core.create("chartdiv", am4charts.XYChart);

chart.data = generateData();

var dateAxis = chart.xAxes.push(new am4charts.DateAxis());
dateAxis.renderer.grid.template.location = 0;
dateAxis.renderer.minGridDistance = 50;
dateAxis.baseInterval = {
  "timeUnit": "day",
  "count": 1
};
dateAxis.skipEmptyPeriods = true;

var valueAxis = chart.yAxes.push(new am4charts.ValueAxis());

var series = chart.series.push(new am4charts.LineSeries());
series.dataFields.valueY = "value";
series.dataFields.dateX = "date";
series.tooltipText = "{dateX}: [b]{valueY}[/]";
series.strokeWidth = 2; 

function generateData() {
  var data = [];
  var firstDate = new Date(2015, 11, 31);
  var i;
  for (i = 0;  i < 15;  ++i) {
    var nextDate = new Date(firstDate);
    nextDate.setDate(nextDate.getDate() + (7 * i));
    data.push({
      "date": nextDate,
      "value": Math.floor(Math.random() * 100 + 1 * i)
    });
  }
  return data;
}

chart.cursor = new am4charts.XYCursor();

#chartdiv {
  width: 100%;
  height: 350px;
}

<script src="//www.amcharts.com/lib/4/core.js"></script>
<script src="//www.amcharts.com/lib/4/charts.js"></script>
<div id="chartdiv"></div>