Creating a Preferences Item Number using Float instead of Int

[Starexify]

I am trying to create an createPrefItemNumber but I can't figure out how to change the formatter to use a Float instead.
I found only this in the Source of the game:

/**
   * Creates a pref item that works with general numbers
   * @param onChange Gets called every time the player changes the value; use this to apply the value
   * @param valueFormatter Will get called every time the game needs to display the float value; use this to change how the displayed value looks
   * @param defaultValue The value that is loaded in when the pref item is created (usually your Preferences.settingVariable)
   * @param min Minimum value (example: 0)
   * @param max Maximum value (example: 10)
   * @param step The value to increment/decrement by (default = 0.1)
   * @param precision Rounds decimals up to a `precision` amount of digits (ex: 4 -> 0.1234, 2 -> 0.12)
   */
  function createPrefItemNumber(prefName:String, prefDesc:String, onChange:Float->Void, ?valueFormatter:Float->String, defaultValue:Int, min:Int, max:Int,
      step:Float = 0.1, precision:Int):Void
  {
    var item = new NumberPreferenceItem(0, (120 * items.length) + 30, prefName, defaultValue, min, max, step, precision, onChange, valueFormatter);
    items.addItem(prefName, item);
    preferenceItems.add(item.lefthandText);
  }

But I can't figure out how to change the valueFormatter to format value as Float.
I have only this till now if helps:

preferences.createPrefItemNumber("Float", "", function(value:Float) {
  save.data.floatFactor = value; 
}, null, save.data.floatFactor , 0, 999, 0.1, 1);

Update:
I tried something like this but now when I force restart (F5) the game the value starts from the int instead of the float, ex: I save 3.3 REFRESH it shows 3.3 but when i change it starts back from 3

preferences.createPrefItemNumber("Float", "", function (value:Float) {
save.data.floatFactor = value; },
function (value:Float):String {
Std.parseFloat(save.data.floatFactor ); }, save.data.floatFactor , 0.0, 1.0, 0.1, 1);