How to use a js function inside $.getJSON?

Question

how can I use my function JSONtoDate inside $.getJSON? This doesn´t work... val.timePosted return a string like 1448038589396, this work fine without the function but when I trying use the function to convert the str to date everything disappear

$(document).ready(function() {

    function JSONtoDate(num){
      var month = num.getMonth() + 1;
      var day = num.getDate();
      var year = num.getFullYear();
      var date = day + "/" + month + "/" + year;
      return(date);
    }

      $.getJSON("http://www.freecodecamp.com/news/hot", function(json) {

        var html = "";
        var count = 0;

        json.map(function(val) {

          if(count == 0){
            html += "<div class = 'row' >";
          }

          html += "<div class = 'stories col-md-3'>";
          html += "<a href = " + val.link + " > <img src = " + val.image + " width = ' 200px'>";
          html += "<p>" + val.headline + "</p> </a>";
          html += "<p>" + val.rank + "</p>";
          html += "<p>" + JSONtoDate(val.timePosted) + "</p>"; 
          html += "</div>";

          count += 1;

          if(count == 4){
            html += "</div>";
            count = 0 ;
          }

        });

        $(".section").html(html);

      });
    });

Answer 1

You have a JS error here:

1448038589396 is not a Date Object and it throws :

Uncaught TypeError: num.getMonth is not a function

try the following in jsFiddle

in JSONtoDate try the following

function JSONtoDate(num){
  var num = new Date(num);
  var month = num.getMonth() + 1;
  var day = num.getDate();
  var year = num.getFullYear();
  var date = day + "/" + month + "/" + year;
  return date;
}

http://jsfiddle.net/Lbt9jy8c/

I converted a string to UNIX timestamp based new Date() Object

Answer 2

Your function JSONtoDate expects a Date object as parameter, but you provide a String - "1448038589396" . You can either pass a date, constructed from the Number value val.timePosted

html += "<p>" + JSONtoDate(new Date(parseInt(val.timePosted))) + "</p>";
                           ^^^^^^^^^^^^^^^^^^              ^^

or let your function accept a string parameter:

function JSONtoDate (dateString) {
  var date = new Date(parseInt(dateString));
  var month = date.getMonth() + 1;
  ...