How to subtract javascriptserializer datetime from current date and find how many minutes/hours ago post was made?

  datetime, javascript, json
        "source": "Home -",
        "pubDate": 1608864230000,
        "read": false,
        "isTagged": false,
        "hasData": false,

From this date I want to find out how many minutes, hours, days ago the news was created. I am not sure about the date format here. maybe javascriptserializer. Platform: react.

Source: Ask Javascript Questions