for me all the combinations worked fine with below code snipplet ,
the snippet is for Angular-2 implementation ,
if you need to add days , pass positive numberofDays , if you need to substract pass negative numberofDays
function addSubstractDays(date: Date, numberofDays: number): Date {
let d = new Date(date);
return new Date(
d.getFullYear(),
d.getMonth(),
(d.getDate() + numberofDays)
);
}