Script.js

$(document).ready(function() {
  $(".authentication").hide();
  $(".message").hide();

  $.ajax({
    url: "chat.php",
    cache: false,
    type: "POST",
    data: { get: true },
    success: function(data) {
      $(".messages").html(data);
    }
  });

  $("#login").click(function() {
    $.ajax({
      url: "authentication.php",
      cache: false,
      type: "POST",
      data: { clicked: 0, username: $(".login-username").val(), password: $(".login-password").val() },
      success: function(data) {
        if (!data.includes("try again")) {
          location.reload();
        } else {
          $(".message").html(data);
          $(".message").slideDown();
        }
      }
    });
  });

  $("#register").click(function() {
    $.ajax({
      url: "authentication.php",
      cache: false,
      type: "POST",
      data: { clicked: 1, username: $(".register-username").val(), password: $(".register-password").val(), confirmPassword: $(".confirm-password").val() },
      success: function(data) {
        if (data.includes("Success")) {
          location.reload();
        } else {
          $(".message").html(data);
          $(".message").slideDown();
        }
      }
    });
  });

  $("#send").click(function() {
    $.ajax({
      url: "chat.php",
      cache: false,
      type: "POST",
      data: { get: false, message: $("#message").val() },
      success: function(data) {
        if (data.includes("login")) {
          $(".authentication").slideDown();
        }
        $(".messages").html(data);
      }
    });
  });
});

$("#logout").click(function() {
  $.ajax({
    url: "authentication.php",
    cache: false,
    type: "POST",
    data: { clicked: 2 },
    success: function(data) {
      location.reload();
    }
  });
});

$("#authentication").click(function() {
  $(".authentication").slideToggle();
});