You are likely over complicating things.
You have a few options but you can just do something like
data.MileStoneDate.getMonth() + "/" + data.MileStoneDate.getDate() + "/" + data.MileStoneDate.getFullYear()
There are other libraries that make formatting dates more "enjoyable" but this would be one of a ton of ways to accomplish what you need. If that doesn't work, a simple google search (like the one provided) will surely provide you what you need.