这应该起作用，您必须先获取属性值才能进行设置

function upDate(previewPic){
    var x = document.getElementById("image").getAttribute('alt')
    document.getElementById("image").innerHTML= x;
}

你能试试吗

 <img class = "preview" alt = "Styling with a Bandana" src = "img.jpg" onmouseover = "upDate(this);">
<div id="image">

</div><!--  -->

<script>
function upDate(previewPic){
    document.getElementById("image").innerHTML=previewPic.alt;
}</script>

您需要在mouseover元素上附加img事件侦听器，并获取alt标签的img属性的值。

const div = document.getElementById('target');
const image = document.getElementById('image');

image.addEventListener('mouseover',(e) => {
  div.innerHTML = image.getAttribute('alt');
});

image.addEventListener('mouseout',(e) => {
  div.innerHTML = ''
});

body {
  display: flex;
  justify-content: space-around;
}

#target {
  height: 100px;
  width: 100px;
  border: 1px solid;
}

<img src="https://picsum.photos/id/237/150/150" alt="dog" id="image"/>
<div id="target"></div>

您可以尝试使用此代码

  function upDate(previewPic){
   var image = document.getElementById("YourimgId");
   document.getElementById("image").innerHTML= image.getAttribute("alt");
}

我认为您没有定义Image标签的ID 参考：https://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_element_innerhtml 另外，alter消息具有另一个div标签。这对于获得清晰的输出效果更好