在span中设置屏幕中心的位图

<span id="mySpan"></span>

#mySpan {
  display: block;
  width: 100%;
  height: 100%;
}

var span = document.getElementById("mySpan");
var img = new Image();
img.src = "path/to/your/image.jpg"; // 替换为你的位图路径
img.onload = function() {
  var screenWidth = window.innerWidth || document.documentElement.clientWidth || document.body.clientWidth;
  var screenHeight = window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight;
  var imageWidth = img.width;
  var imageHeight = img.height;
  
  // 计算位图在屏幕中心的位置
  var left = (screenWidth - imageWidth) / 2;
  var top = (screenHeight - imageHeight) / 2;
  
  // 设置位图的位置
  img.style.position = "absolute";
  img.style.left = left + "px";
  img.style.top = top + "px";
  
  // 将位图插入到span元素中
  span.appendChild(img);
};