How to submit form data in the same page in WordPress without reloading the page?

Question

I have a custom PHP template - form. I'm trying to send this form in the same page using AJAX without reloading the page. Hide the form after submission and display the thank you message. This form is displayed in a modal. But what happens is that the page is still reloading.

HTML

<form method="POST" action="" name="modalForm" id="modalForm" enctype="multipart/form-data" autocomplete="off">
        <input placeholder="Last Name*" type="text" name="lastName" id="lastName" value="" required>
        <label class="error" for="name" id="lastName_error">This field is required.</label>
        <input placeholder="First Name*" type="text" name="firstName" id="firstName" value="" required>
        <label class="error" for="name" id="firstName_error">This field is required.</label>
        <input placeholder="Email Address" type="email" name="Email" id="Email" onblur="this.setAttribute('value', this.value);" value="" required>
        <label class="error" for="email" id="email_error">This field is required.</label>
        <span class="validation-text">Please enter a valid email address.</span>
        <input placeholder="Mobile Number*" type="text" name="contactNumber" id="contactNumber" onkeypress="return isNumberKey(event)" value="" size="11" minlength="11" maxlength="11" pattern ="^09\d{9}$" required>
        <label class="error" for="contactNumber" id="contactNumber_error">This field is required.</label>
        <input type="submit" name="submit" value="Submit" id="form-submit">
</form>

JS

    (function($) {
    $('.error').hide();
    $(".button").click(function() {
      // validate and process form here

      $('.error').hide();
        var name = $("input#lastName").val();
        if (lastName == "") {
        $("label#lastName_error").show();
        $("input#lastName").focus();
        return false;
      }
        var name = $("input#firstName").val();
        if (lastName == "") {
        $("label#firstName_error").show();
        $("input#firstName").focus();
        return false;
      }
        var email = $("input#Email").val();
        if (Email == "") {
        $("label#email_error").show();
        $("input#Email").focus();
        return false;
      }
        var phone = $("input#contactNumber").val();
        if (contactNumber == "") {
        $("label#contactNumber_error").show();
        $("input#contactNumber").focus();
        return false;
      }

    });

    var dataString = 'lastName='+ lastName + '&Email=' + Email + '&contactNumber=' + contactNumber;
  //alert (dataString);return false;
  $.ajax({
    type: "POST",
    url: "/wordpress-page/",
    data: dataString,
    success: function() {
      $('#modalForm').html("<div id='message'></div>");
      $('#message').html("<h2>Contact Form Submitted!</h2>")
      .append("<p>We will be in touch soon.</p>")
      .hide()
      .fadeIn(1500, function() {
        $('#message').append("<img id='checkmark' src='images/check.png' />");
      });
    }
  });
  return false;
});

Answer 1

I created a fiddle with your code and with the fixed code.

1. The whole code runs as soon as possible, but should run after the DOM is ready, so that the selectors can match DOM-elements: (function($) { should be changed to ($(document).ready(function(){

2. Your selector $('.button') does not match any elements, in your case it should match the submit-button $('#form-submit')

3. I would add preventDefault() to make sure the default action of the submit button (submitting the form) won't happen.

4. The form validation is really messed up. You are checking a variables that are not set.

5. Your dataString also uses unset variables. (First name is also missing.)

I exchanged the ajax call for a console.log to dump the data, but kept the success-function.

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There are so many small errors in your code, that it looks like you copied it from different sources without doing much debugging before asking this question.

Try debugging step by step as you write your code.