Ionic date format issue in birth date


Hi Dear ,
I want to ask you about a question related to date format in ionic. I have two diffrent kind of mobile’ one is Redmi Note 4 (MI) 2. oppo
first one redmi there is no feature to change date format. it show’s the date format by default in DD/MM/YYYY.
Next second is oppo :There is the feature to change date format is available. it’s by-default format is Regional (12/31/2017)
other format available or changeable in the list like

The question is that when i run the build in my redmi note 4 format by default going on dd/mm/yyyy
i choose on contact from the contact-list my birthday is 01/01/1990

But when same build i does use in other mobile like opps it shows me my birthday 12/31/1989.
(I also saw the format change like dd/mm/yyyy. but still have bug)

It shows me big diffrence, Why is this happening. Please answer me, soon. I’m curious to know that.

Redmi Note 4