Ionic / Angular DatePicker programmatically change value

I am now using the plain HTML5-style datepicker by adding type="date" to the input-element. This looks good and works with picking dates and using them. But I want to be able to set the value of the datepicker programmatically, to enforce ranges the user is able to choose from.

The element now looks like this:

<input type="date" 
  placeholder="Choose startdate" 
  ng-model="rangeStart"
  ng-change="changeRangeStart(rangeStart)"
>

There is also a button to reset the date to today, for example. This is how I try to do that:

// today is a Date-object
$scope.rangeStart = today;

EDIT// ^ changed rangeEnd to rangeStart (typo)

Anyone who can help me with this? Now the user can set the date, but I want to be able to change the date for the user.