如何仅显示对象中的可用属性？

In the eventRender method from fullcalendar, in the text that gets rendered I would like to only show the attributes from the event object that are available i.e not undefined.

As you can see below, it tries to show every attribute of the event object, where if the attribute is undefined it'll render undefined:

eventRender: function(event, element) {

    $(element).qtip({

        style: {
            classes: 'myStyle',
            height: 150,
            width: 300,
            textAlign: 'center',
        },

        content: {
            title: event.room_id,

            text: "description: " + event.description + "<br/>" +
                  "number: " + event.capacity + "<br/>" + 
                  "Name: " + event.name + "<br/>" + 
                  "Role: " + event.role + "<br/>" + 
                  "Rank: " + event.sub_role + "<br/>" +
                  "Hours: " + event.hours + "<br/>",
        }
    })
}

You can go through the event properties and build the tooltip text

https://jsfiddle.net/j9x06z7s/

$('#calendar').fullCalendar({
  events: [{
    start: moment(), // required, should not show in tip
    title: "Required title event 1", // required, should not show in tip
    room_id: "Room 1",
    description: "Description for event 1",
    capacity: 10,
    name: "Name 1",
    role: "Role event 1",
    sub_role: "Rank event 1",
    hours: 1,
  }, {
    start: moment().add(1, 'day'), // required, should not show in tip
    title: "Required title event 2", // required, should not show in tip
    room_id: "Room 2",
    description: "Description for event 2",
    //capacity: 20, // should not show in tip
    name: "Name 2",
    //role: "Role event 2", // should not show in tip
    sub_role: "Rank event 2",
    hours: 2,
  }, {
    start: moment().add(2, 'day'), // required, should not show in tip
    title: "Required title event 3", // required, should not show in tip
    room_id: "Room 3",
    description: "Description for event 3",
    capacity: 30,
    name: "", // should not show in tip
    role: undefined, // should not show in tip
    sub_role: [], // should not show in tip
    hours: 3,
  }],
  eventRender: function(event, element) {
    $(element).qtip({
      style: {
        classes: 'myStyle',
        height: 150,
        width: 300,
        textAlign: 'center',
      },
      content: {
        title: event.room_id,
        text: build_text(event)
      }
    });
  }
});

function build_text(event) {
  var text = "";
  // go through event properties
  $.each(event, function(key, value) {
    // is it a key we care about for tooltip?
    if (["description", "capacity", "name", "role", "sub_role", "hours"].includes(key)
      // does it have a value?
      && (value != null && value != "")) {
      text += key + ": " + value + "<br/>";
    }
  });
  return text;
}