Andrew

$("document").ready(function(){
            
            $("#btn").click(function(){

                var title = $("#title").val();
                var description = $("#description").val();
                var texting = $("#texting").val();

                $("#title").val('');
                $("#description").val('');
                $("#texting").val('');

                $.ajax({
                    url: '../Model/AddPost.php',
                    type: 'POST',
                    data: {title:title, description:description, texting:texting},
                    success: function(data){
                        // alert(data);
                    }
                });

                $.ajax ({
                        type: "POST",
                        url: '../Model/AddPost.php',
                        data: {title:title, description:description, texting:texting},
                        success: function(data){
                            $("#textpost").html(data);
                        }
                });

            });

        });

$("document").ready(function(){
            
            $("#form").submit(function(e){
e.preventDefault();
                var title = $("#title").val();
                var description = $("#description").val();
                var texting = $("#texting").val();

                $("#title").val('');
                $("#description").val('');
                $("#texting").val('');
                $.ajax ({
                        type: "POST",
                        url: '../Model/AddPost.php',
                        data: {title:title, description:description, texting:texting},
                        success: function(data){
                            $("#textpost").html(data);
                        }
                });

            });

        });

<form method="post" class="auth-form">
  <input type="text" name="login" placeholder="login" id="login">
  <input type="password" name="password" placeholder="password" id="password">
  <button id="submitBtn">Send</button>
</form>

const submitBtnElem = document.getElementById('submitBtn');

  if(submitBtnElem) {
    submitBtnElem.addEventListener('click', auth(e));
  }

  function auth(e) {
e.preventDefault();
    const login = document.getElementById('login').value;
    const password = document.getElementById('password').value;		
    const xhr = new XMLHttpRequest();
    xhr.open("POST", "auth_request", true);
    xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    xhr.onreadystatechange = function() {
      if (this.readyState != 4) return;
      console.log( this.responseText );
    }
    xhr.send(`login=${login}&password=${password}`);
  }