How to set system date properties(Target Start & Target finish) dynamically?

Hello Team,

I am trying to set the project template Target start and target finish property dynamically(date_start_target & date_start_due).

I am able to set date in field using following code.

Picture 1

//Getting today's date
var Todaysdate = new Date();

//Getting date in dd/MM/yyy format
var Currentdate = Todaysdate.getDate() + "/"
+ (Todaysdate.getMonth()+1) + "/"
+ Todaysdate.getFullYear();

//alert(Currentdate);

var newdate = new Date(Todaysdate);

//Setting Next day date
newdate.setDate(newdate.getDate() + 1);

//Getting date in dd/MM/yyy format
var NextDate = newdate.getDate() + "/"
+ (newdate.getMonth()+1) + "/"
+ newdate.getFullYear();
//alert(NextDate);

//Setting Project Target Start and Target Finish property with new values.
window.handleItemChange("date_start_target",Currentdate);
window.handleItemChange("date_due_target",NextDate);

On click of saving project it give following error

Picture 2

I am not getting which format is required.

Can any one please help me out?