如何显示无模式对话框并立即显示信息？

alert("欢迎来到我们的网站！");

<div id="myModal" class="modal">
  <div class="modal-content">
    <span class="close">&times;</span>
    <p>欢迎来到我们的网站！</p>
  </div>
</div>

.modal {
  display: none;
  position: fixed;
  z-index: 1;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  overflow: auto;
  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: #aaaaaa;
  float: right;
  font-size: 28px;
  font-weight: bold;
}

.close:hover,
.close:focus {
  color: #000;
  text-decoration: none;
  cursor: pointer;
}

window.onload = function() {
  var modal = document.getElementById("myModal");
  var span = document.getElementsByClassName("close")[0];

  modal.style.display = "block";

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

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