js中提示消息框

alert("这是一个警告消息！");

if (confirm("你确定要删除这条记录吗？")) {
    // 用户点击了“确定”
    // 执行删除操作
} else {
    // 用户点击了“取消”
    // 不执行任何操作或给出其他提示
}

let userInput = prompt("请输入你的名字：");
if (userInput !== null) {
    alert("你好，" + userInput + "!");
} else {
    alert("你没有输入名字。");
}

<!-- HTML -->
<div id="myModal" class="modal">
  <div class="modal-content">
    <span class="close">&times;</span>
    <p>这是一个自定义消息框！</p>
    <button id="confirmBtn">确定</button>
  </div>
</div>

<!-- CSS -->
<style>
.modal {
  display: none; 
  position: fixed; 
  z-index: 1; 
  left: 0;
  top: 0;
  width: 100%; 
  height: 100%; 
  overflow: auto; 
  background-color: rgb(0,0,0); 
  background-color: rgba(0,0,0,0.4); 
}

.modal-content {
  background-color: #fefefe;
  margin: 15% auto; 
  padding: 20px;
  border: 1px solid #888;
  width: 80%; 
}

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

.close:hover,
.close:focus {
  color: black;
  text-decoration: none;
  cursor: pointer;
}
</style>

<!-- JavaScript -->
<script>
var modal = document.getElementById("myModal");
var span = document.getElementsByClassName("close")[0];
var confirmBtn = document.getElementById("confirmBtn");

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

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

confirmBtn.onclick = function() {
  modal.style.display = "none";
  // 执行确定后的操作
}

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

// 调用显示模态框的函数
showModal();
</script>