validation for form is working,but popup box is not working HTML,Javascript

i want a popup box with link to home page by clicking submit button only after validation.

How to create a popup box with a link to home page, triggered by a submit button only after validation in HTML, and JavaScript?

validation is working in this form but popbox is not working.
i cnt find why this is not working?

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

var subObject = {
  "place1": ["place1", "place2", "place3"],
  "place2": ["place4", "place4"],
}


window.onload = function() {

  var distSel = document.getElementById("district");
  var citySel = document.getElementById("city");

  for (var x in subObject) {
    distSel.options[distSel.options.length] = new Option(x, x);
  }
  distSel.onchange = function() {

    citySel.length = 1;


    var z = subObject[distSel.value];
    for (var i = 0; i < z.length; i++) {
      citySel.options[citySel.options.length] = new Option(z[i], z[i]);
    }
  }
}

function valid() {

  var modal = document.getElementById("myModal");
  var btn = document.getElementById("myBtn");
  var span = document.getElementsByClassName("close")[0];



  if (f1.username.value == "") {
    alert('enter the name');
    f1.username.focus();
    return false;
  } else if (f1.date.value == "") {
    alert('enter your date of birth');
    f1.date.focus();
    return false;
  } else if (f1.gender.value == "") {
    alert('Select gender');
    f1.gender.focus();
    return false;
  } else if (f1.district.value == "") {
    alert('select your district');
    f1.district.focus();
    return false;
  } else if (f1.city.value == "") {
    alert('select your city');
    f1.city.focus();
    return false;
  } else {



    btn.onclick = function() {
      modal.style.display = "block";
    }

    span.onclick = function() {
      modal.style.display = "none";
    }


    window.onclick = function(event) {
      if (event.target == modal) {
        modal.style.display = "none";
      }
    }

  }
}

<!-- language: lang-css -->

body {
  font-family: Arial, Helvetica, sans-serif;
}

form {
  border: 3px solid #f1f1f1;
}

input[type=text],
input[type=date] {
  width: 75%;
  padding: 5px 10px;
  margin: 8px 0;
  display: inline-block;
  border: 1px solid #ccc;
  box-sizing: border-box;
}

button {
  background-color: #FF5733;
  color: white;
  padding: 10px 15px;
  margin: 8px 0;
  border: none;
  cursor: pointer;
  width: 100px;
  border-radius: 15px;
}

button:hover {
  opacity: 0.8;
}

select {
  height: 30px;
  width: 75%;
  padding: 0 15px;
  text-align: center;
}

form {
  padding-left: 290px;
}

body {
  font-family: Arial, Helvetica, sans-serif;
}


/* The Modal (background) */

.modal {
  display: none;
  /* Hidden by default */
  position: fixed;
  /* Stay in place */
  z-index: 1;
  /* Sit on top */
  padding-top: 100px;
  /* Location of the box */
  left: 0;
  top: 0;
  width: 100%;
  /* Full width */
  height: 100%;
  /* Full height */
  overflow: auto;
  /* Enable scroll if needed */
  background-color: rgb(0, 0, 0);
  /* Fallback color */
  background-color: rgba(0, 0, 0, 0.4);
  /* Black w/ opacity */
}


/* Modal Content */

.modal-content {
  position: relative;
  background-color: #fefefe;
  margin: auto;
  padding: 0;
  border: 1px solid #888;
  width: 50%;
  box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
  -webkit-animation-name: animatetop;
  -webkit-animation-duration: 0.4s;
  animation-name: animatetop;
  animation-duration: 0.4s
}


/* Add Animation */

@-webkit-keyframes animatetop {
  from {
    top: -300px;
    opacity: 0
  }
  to {
    top: 0;
    opacity: 1
  }
}

@keyframes animatetop {
  from {
    top: -300px;
    opacity: 0
  }
  to {
    top: 0;
    opacity: 1
  }
}


/* The Close Button */

.close {
  color: white;
  float: right;
  font-size: 28px;
  font-weight: bold;
}

.close:hover,
.close:focus {
  color: #000;
  text-decoration: none;
  cursor: pointer;
}

.modal-header {
  padding: 10px 15px;
  background-color: #5cb85c;
  color: white;
}

.modal-body {
  padding: 10px 15px;
  text-align: center;
}

<!-- language: lang-html -->

<!--model div open-->

<div id="myModal" class="modal">
  <div class="modal-content">
    <div class="modal-header">

      <h2>Application Accepted</h2>
      <span class="close">×</span>
    </div>
    <div class="modal-body">
      <p>Go Back To Home Page <a href="home">Home</a></p>
    </div>
  </div>
</div>
<!--model div close-->


Form code:

<form method="post" name="f1" action="">


  <h2 style="padding-left:50px">Application Form</h2>
  <table>
    <tr>
      <td>
        <label for="uname">Name</label>
      </td>
      <td>
        <input type="text" id="uname" name="username" required>
      </td>
    </tr>
    <tr>
      <td>
        <label for="date">Date Of Birth</label>
      </td>
      <td>
        <input type="date" id="date" name="date" required> </td>
    </tr>



    <tr>
      <td>
        <label>Gender</label>
      </td>
      <td>
        <label>
                    <input type="radio" value="female" name="gender" required> Female</label>
        <label>
                    <input value="male" type="radio" name="gender"> Male</label>
      </td>
    </tr>





    <tr>
      <td>
        <label for="district">District</label>
      </td>
      <td>
        <select name="district" id="district">
          <option value="">---Select District---</option>
        </select>
      </td>
    </tr>

    <tr>
      <td>
        <label for="city">City</label>
      </td>
      <td>
        <select name="city" id="city">
          <option value="">---Select District First---</option>
        </select>
      </td>
    </tr>



    <tr>
      <td></td>
      <td>




        <button type="submit" id="myBtn" class="cancelbtn" onclick="return valid()">SUBMIT</button>



      </td>
    </tr>
  </table>
</form>

<!-- end snippet -->

You are adding event handlers in your else part in valid function you just need to show the modal in the else.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

var subObject = {
  "place1": ["place1", "place2", "place3"],
  "place2": ["place4", "place4"],
}


window.onload = function() {

  var distSel = document.getElementById("district");
  var citySel = document.getElementById("city");

  for (var x in subObject) {
    distSel.options[distSel.options.length] = new Option(x, x);
  }
  distSel.onchange = function() {

    citySel.length = 1;


    var z = subObject[distSel.value];
    for (var i = 0; i < z.length; i++) {
      citySel.options[citySel.options.length] = new Option(z[i], z[i]);
    }
  }
}

var modal = document.getElementById("myModal");
var btn = document.getElementById("myBtn");
var span = document.getElementsByClassName("close")[0];

span.onclick = function() {
  modal.style.display = "none";
}

window.onclick = function(event) {
  if (event.target == modal) {
    modal.style.display = "none";
  }
}

function valid() {
  if (f1.username.value == "") {
    alert('enter the name');
    f1.username.focus();
    return false;
  } else if (f1.date.value == "") {
    alert('enter your date of birth');
    f1.date.focus();
    return false;
  } else if (f1.gender.value == "") {
    alert('Select gender');
    f1.gender.focus();
    return false;
  } else if (f1.district.value == "") {
    alert('select your district');
    f1.district.focus();
    return false;
  } else if (f1.city.value == "") {
    alert('select your city');
    f1.city.focus();
    return false;
  } else {
    modal.style.display = "block";
    return false; // added return false here because form will try to refresh and submit at this point.
  }
}

<!-- language: lang-css -->

body {
  font-family: Arial, Helvetica, sans-serif;
}

form {
  border: 3px solid #f1f1f1;
}

input[type=text],
input[type=date] {
  width: 75%;
  padding: 5px 10px;
  margin: 8px 0;
  display: inline-block;
  border: 1px solid #ccc;
  box-sizing: border-box;
}

button {
  background-color: #FF5733;
  color: white;
  padding: 10px 15px;
  margin: 8px 0;
  border: none;
  cursor: pointer;
  width: 100px;
  border-radius: 15px;
}

button:hover {
  opacity: 0.8;
}

select {
  height: 30px;
  width: 75%;
  padding: 0 15px;
  text-align: center;
}

form {
  padding-left: 290px;
}

body {
  font-family: Arial, Helvetica, sans-serif;
}


/* The Modal (background) */

.modal {
  display: none;
  /* Hidden by default */
  position: fixed;
  /* Stay in place */
  z-index: 1;
  /* Sit on top */
  padding-top: 100px;
  /* Location of the box */
  left: 0;
  top: 0;
  width: 100%;
  /* Full width */
  height: 100%;
  /* Full height */
  overflow: auto;
  /* Enable scroll if needed */
  background-color: rgb(0, 0, 0);
  /* Fallback color */
  background-color: rgba(0, 0, 0, 0.4);
  /* Black w/ opacity */
}


/* Modal Content */

.modal-content {
  position: relative;
  background-color: #fefefe;
  margin: auto;
  padding: 0;
  border: 1px solid #888;
  width: 50%;
  box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
  -webkit-animation-name: animatetop;
  -webkit-animation-duration: 0.4s;
  animation-name: animatetop;
  animation-duration: 0.4s
}


/* Add Animation */

@-webkit-keyframes animatetop {
  from {
    top: -300px;
    opacity: 0
  }
  to {
    top: 0;
    opacity: 1
  }
}

@keyframes animatetop {
  from {
    top: -300px;
    opacity: 0
  }
  to {
    top: 0;
    opacity: 1
  }
}


/* The Close Button */

.close {
  color: white;
  float: right;
  font-size: 28px;
  font-weight: bold;
}

.close:hover,
.close:focus {
  color: #000;
  text-decoration: none;
  cursor: pointer;
}

.modal-header {
  padding: 10px 15px;
  background-color: #5cb85c;
  color: white;
}

.modal-body {
  padding: 10px 15px;
  text-align: center;
}

<!-- language: lang-html -->

<!--model div open-->

<div id="myModal" class="modal">
  <div class="modal-content">
    <div class="modal-header">

      <h2>Application Accepted</h2>
      <span class="close">×</span>
    </div>
    <div class="modal-body">
      <p>Go Back To Home Page <a href="home">Home</a></p>
    </div>
  </div>
</div>
<!--model div close-->

<form method="post" name="f1" action="">


  <h2 style="padding-left:50px">Application Form</h2>
  <table>
    <tr>
      <td>
        <label for="uname">Name</label>
      </td>
      <td>
        <input type="text" id="uname" name="username" required>
      </td>
    </tr>
    <tr>
      <td>
        <label for="date">Date Of Birth</label>
      </td>
      <td>
        <input type="date" id="date" name="date" required> </td>
    </tr>



    <tr>
      <td>
        <label>Gender</label>
      </td>
      <td>
        <label>
          <input type="radio" value="female" name="gender" required> Female</label>
        <label>
          <input value="male" type="radio" name="gender"> Male</label>
      </td>
    </tr>





    <tr>
      <td>
        <label for="district">District</label>
      </td>
      <td>
        <select name="district" id="district">
          <option value="">---Select District---</option>
        </select>
      </td>
    </tr>

    <tr>
      <td>
        <label for="city">City</label>
      </td>
      <td>
        <select name="city" id="city">
          <option value="">---Select District First---</option>
        </select>
      </td>
    </tr>



    <tr>
      <td></td>
      <td>




        <button type="submit" id="myBtn" class="cancelbtn" onclick="return valid();">SUBMIT</button>



      </td>
    </tr>
  </table>
</form>

<!-- end snippet -->