The code posted above had like 4 anti-patterns in it. Do not attempt anything inside it.
Put a break point in your subscribe and see what data is. If it’s json you need json.parse to turn it from a string into an array (although the"json" you posted looks invalid because there are no array brackets around it.
I’m assuming your date strings there are year month day, I could be wrong. Also you could still get timezone issues from this, it may be worth it for you to use a date library. However, you possibly want something like this: https://jsfiddle.net/po8a111o/11/
EDIT: If you can’t figure it out from this you need to post your restProvider.getJson method, because as it stands there is no way anyone could ever know what data you are actually working with