Dynamic data disappearing on adding

I've a form to add External User in which 2 of the fields are not mandatory by default. However, they become mandatory only if one of those fields are filled out. On clicking the apply button, the content of my form is used to generate a dynamic div which gets appended to the 'div.container'. However, it is just disappearing as soon as it is added.

What could be the reason for it?

Here's the code:

var currentPageNo = 0; // Keep track of currently displayed page


// Select button that is descendant of userList
$('#userList .prev-btn').click(function(){ 
    userList(currentPageNo-10);
});
$('#userList .next-btn').click(function(){ 
    userList(currentPageNo+10);
});
$('#adminList .prev-btn').click(function(){ 
    adminList(currentPageNo-10);
});
$('#adminList .next-btn').click(function(){ 
    adminList(currentPageNo+10);
});

function userList(pageNo) {
    var resType="userList";
    createTable(resType,pageNo);
}

function adminList(pageNo) {
    var resType="adminList";
    createTable(resType,pageNo);
}

function createTable(resType, pageNo) {
    // Update global variable
    currentPageNo = pageNo; 
    // Set visibility of the correct "prev" button:
    $('#' + resType + ' .prev-btn').toggle(pageNo > 0);
    // Ask one record more than needed, to determine if there are more records after this page:
    $.getJSON("https://api.randomuser.me/?results=11&resType="+resType + "&pageIndex=" + pageNo, function(data) {
        var $table = $('#' + resType + ' table');
        $('tr:has(td)', $table).empty();
        // Check if there's an extra record which we do not display, 
        // but determines that there is a next page
        $('#' + resType + ' .next-btn').toggle(data.results.length > 10);
        // Slice results, so 11th record is not included:
        data.results.slice(0, 10).forEach(function (record, i) { // add second argument for numbering records
            var json = JSON.stringify(record);
            $table.append(
                $('<tr>').append(
                    $('<td>').append(
                        $('<input>').attr('type', 'checkbox')
                                    .addClass('selectRow')
                                    .val(json),
                        (i+1+pageNo) // display row number
                    ),
                    $('<td>').append(
                        $('<a>').attr('href', record.picture.thumbnail)
                                .addClass('imgurl')
                                .attr('target', '_blank')
                                .text(record.name.first)
                    ),
                    $('<td>').append(record.dob)
                )
            );
        });
        // Show the prev and/or buttons
        
        
    }).fail(function(error) {
        console.log("**********AJAX ERROR: " + error);
    });            
}

var savedData = []; // The objects as array, so to have an order.

function saveData(){
    var errors = [];
    // Add selected to map
    $('input.selectRow:checked').each(function(count) {
        // Get the JSON that is stored as value for the checkbox
        var obj = JSON.parse($(this).val());
        // See if this URL was already collected (that's easy with Set)
        if (savedData.find(record => record.picture.thumbnail === obj.picture.thumbnail)) {
            errors.push(obj.name.first);
        } else {
            // Append it
            savedData.push(obj);
        }
    });
    refreshDisplay();
    if (errors.length) {
        alert('The following were already selected:\n' + errors.join('\n'));
    }
}

function refreshDisplay() {
    $('.container').html('');
    savedData.forEach(function (obj) {
        // Reset container, and append collected data (use jQuery for appending)
        $('.container').append(
            $('<div>').addClass('parent').append(
                $('<label>').addClass('dataLabel').text('Name: '),
                obj.name.first + ' ' + obj.name.last,
                $('<br>'), // line-break between name & pic
                $('<img>').addClass('myLink').attr('src', obj.picture.thumbnail), $('<br>'),
                $('<label>').addClass('dataLabel').text('Date of birth: '),
                obj.dob, $('<br>'),
                $('<label>').addClass('dataLabel').text('Address: '), $('<br>'),
                obj.location.street, $('<br>'),
                obj.location.city + ' ' + obj.location.postcode, $('<br>'),
                obj.location.state, $('<br>'),
                $('<button>').addClass('removeMe').text('Delete'),
                $('<button>').addClass('top-btn').text('Swap with top'),
                $('<button>').addClass('down-btn').text('Swap with down')
            )	
        );
    })
    // Clear checkboxes:
    $('.selectRow').prop('checked', false);
    handleEvents();
}

function logSavedData(){
    // Convert to JSON and log to console. You would instead post it
    // to some URL, or save it to localStorage.
    console.log(JSON.stringify(savedData, null, 2));
}

function getIndex(elem) {
    return $(elem).parent('.parent').index();
}

$(document).on('click', '.removeMe', function() {
    // Delete this from the saved Data
    savedData.splice(getIndex(this), 1);
    // And redisplay
    refreshDisplay();
});

/* Swapping the displayed articles in the result list */
$(document).on('click', ".down-btn", function() {
    var index = getIndex(this);
    // Swap in memory
    savedData.splice(index, 2, savedData[index+1], savedData[index]);
    // And redisplay
    refreshDisplay();
});

$(document).on('click', ".top-btn", function() {
    var index = getIndex(this);
    // Swap in memory
    savedData.splice(index-1, 2, savedData[index], savedData[index-1]);
    // And redisplay
    refreshDisplay();
});
    
/* Disable top & down buttons for the first and the last article respectively in the result list */
function handleEvents() {
    $(".top-btn, .down-btn").prop("disabled", false).show();
    $(".parent:first").find(".top-btn").prop("disabled", true).hide();
    $(".parent:last").find(".down-btn").prop("disabled", true).hide();
}

$(document).ready(function(){
    $('#showExtForm-btn').click(function(){
        $('#extUser').toggle();
    });
	
	var $dob = $('#dob');
	var $myImg = $('#myImg');
	var $formData = $($dob).add($myImg);
	
	$formData.on('change', function(e) {

	  var dob = $dob.val();
	  var myImg = $myImg.val();
	  
	  $formData.prop('required', dob || myImg);
	  
	});
	
    $("#extUserForm").submit(function(e){
        var dob = $dob.val();
		var myImg = $myImg.val();
		
		var dataFilled = !!dob && !!myImg;
		var dataUnfilled = !dob && !myImg;
			  
		if (toolFilled || toolUnfilled) {
			addExtUser();
			return true;
		}
		return false;
   });
});

function addExtUser() {
    var extObj = {
        name: {
            title: "mr", // No ladies? :-)
            first: $("#name").val(),
            // Last name ?
        },
        dob: $("#dob").val(),
        picture: {
            thumbnail: $("#myImg").val()
        },
        location: { // maybe also ask for this info?
        }
    };
    savedData.push(extObj);
    refreshDisplay(); // Will show some undefined stuff (location...)
}

<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.0/jquery.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet"/>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<button class="btn btn-primary btn-sm" data-toggle="modal" data-target="#userList" onclick="userList(0)">User List</button>
<button class="btn btn-primary btn-sm" onclick="logSavedData()">Get Saved Data</button>
<button class="btn btn-primary btn-sm" data-toggle="modal" data-target="#adminList" onclick="adminList(0)">User Admin</button>
<button class="btn btn-primary btn-sm" data-toggle="modal" data-target="#extUser">Open External Form</button>

  <div class="modal fade" id="userList" role="dialog">
    <div class="modal-dialog modal-lg">
    
      
      <div class="modal-content">
        <div class="modal-header">
          <button type="button" class="close" data-dismiss="modal">&times;</button>
          <h4 class="modal-title">User List</h4>
        </div>
        <div class="modal-body">
          <div class="table-responsive">
              <table class="table table-bordered table-hover" id="datatable">
                <tr>
                    <th>Select</th>
                    <th>Name</th>
                    <th>DOB</th>
                </tr>
            </table>
          </div>
          <div class="row">
            <div class="col-sm-offset-3 col-sm-4">
                <button type="button" class="btn btn-primary prev-btn"><span class="glyphicon glyphicon-chevron-left"></span></button>
            </div>

            <div class="col-sm-4">
                <button type="button" class="btn btn-primary next-btn"><span class="glyphicon glyphicon-chevron-right"></span></button>
            </div>
        </div>
            <hr/>
        <div class="row">
            <div class="col-sm-offset-3 col-sm-4">
                <button type="button" class="btn btn-primary btn-sm" onclick="saveData()">Save selected</button>
            </div>
            <div class="col-sm-4">
                <button type="button" class="btn btn-primary btn-sm close-less-modal" data-dismiss="modal">Close</button>
            </div>
        </div>
        <br />
      </div>
    </div>
  </div>
</div>

<div class="modal fade" id="adminList" role="dialog">
    <div class="modal-dialog modal-lg">
      <div class="modal-content">
        <div class="modal-header">
          <button type="button" class="close" data-dismiss="modal">&times;</button>
          <h4 class="modal-title">Admin List</h4>
        </div>
        <div class="modal-body">
          <div class="table-responsive">
              <table class="table table-bordered table-hover" id="datatable">
                <tr>
                    <th>Select</th>
                    <th>Name</th>
                    <th>DOB</th>
                </tr>
            </table>
          </div>
          <div class="row">
            <div class="col-sm-offset-3 col-sm-4">
                <button type="button" class="btn btn-primary prev-btn"><span class="glyphicon glyphicon-chevron-left"></span></button>
            </div>

            <div class="col-sm-4">
                <button type="button" class="btn btn-primary next-btn"><span class="glyphicon glyphicon-chevron-right"></span></button>
            </div>
        </div>
            <hr/>
        <div class="row">
            <div class="col-sm-offset-3 col-sm-4">
                <button type="button" class="btn btn-primary btn-sm" onclick="saveData()">Save selected</button>
            </div>
            <div class="col-sm-4">
                <button type="button" class="btn btn-primary btn-sm close-less-modal" data-dismiss="modal">Close</button>
            </div>
        </div>
        <br />
      </div>
    </div>
  </div>
</div>

<div class="modal fade" id="extUser" role="dialog">
    <div class="modal-dialog modal-lg">
    
      <!-- External User-->
      <div class="modal-content">
        <div class="modal-header">
          <button type="button" class="close" data-dismiss="modal">&times;</button>
          <h4 class="modal-title">Add External User</h4>
        </div>
        <div class="modal-body">
          <form class="form-horizontal" id="extUserForm">
            <div class="form-group">
              <label class="control-label col-sm-3" for="name">Name:</label>
              <div class="col-sm-8">
                <input type="text" class="form-control" id="name" name="name" required>
              </div>
            </div>
            <div class="form-group">
              <label class="control-label col-sm-3" for="myImg">Image:</label>
              <div class="col-sm-8">
                <input type="text" class="form-control" id="myImg" name="myImg">
              </div>
            </div>
                                            
            <div class="form-group">
              <label class="control-label col-sm-3" for="dob">DOB:</label>
              <div class="col-sm-8">
                <input type="date" class="form-control" id="dob" name="dob">
              </div>
            </div>
            <hr />
            <div class="form-group">        
              <div class="col-sm-offset-3 col-sm-3">
                <button class="btn btn-primary btn-sm">Submit</button>
              </div>
              <div class="col-sm-3">
                <button type="reset" class="btn btn-primary btn-sm">Reset</button>
              </div>
              <div class="col-sm-3">
                <button type="button" class="btn btn-primary btn-sm close-external-modal" data-dismiss="modal">Close</button>
              </div>
            </div>
          </form>
        </div> 
      </div>
    </div>
  </div>

<div class="container"></div>

The main issue is in the $("#extUserForm").submit callback where you have:

return true;

This will make the default form-submission effect kick in, i.e. the page will navigate to the form's action attribute, or if there is none (as is your case), the page will reload. That is why you briefly see the entry on the page, just before the page is reloaded, and everything starts from scratch.

So, you must stick with: