JSFiddle - React, Tailwind, and code Playground

HTML

<input id="name" type="text" class="form-control" placeholder="Name" required="">
<input id="email" type="email" class="form-control" placeholder="Email" required="">
<input id="phone" type="text" class="form-control" placeholder="Phone" required="">
<textarea id="message" class="form-control" placeholder="Message" required=""></textarea>
<button type="button" onclick="submit();">Submit ok</button>

JavaScript

function submit() {
  alert("Hello! I am an alert box!!");
  var name = $('#name').val();
  var email = $('#email').val();
  var phone = $('#phone').val();
  var message = $('#message').val();
  console.log("'"+name+"'", "'"+email+"'", "'"+phone+"'")
  if (name == '' || email == '' || phone == '') {
    alert("Please insert Full Name , Email and phone!");
  } else {
    $.ajax({
      type: 'POST',
      url: '?f=send_email',
      data: {
        name: name,
        email: email,
        phone: phone,
        message: message
      },
      success: function(data) {
        if (data == '1') {
          alert("Send Successfull. We will reply you soon.");
          location.reload();
        } else {
          alert("Error while processing data, please try again.");
        }
      }
    });
  }
}