js 将div置中

<div id="myDiv" style="width: 100px; height: 100px; background-color: red;"></div>

function centerDiv() {
  var div = document.getElementById('myDiv');
  var body = document.body;
  var html = document.documentElement;

  // 获取页面宽度和高度
  var pageWidth = Math.max(body.scrollWidth, body.offsetWidth, html.clientWidth, html.scrollWidth, html.offsetWidth);
  var pageHeight = Math.max(body.scrollHeight, body.offsetHeight, html.clientHeight, html.scrollHeight, html.offsetHeight);

  // 获取div的宽度和高度
  var divWidth = div.offsetWidth;
  var divHeight = div.offsetHeight;

  // 计算div应该放置的位置
  var left = (pageWidth - divWidth) / 2;
  var top = (pageHeight - divHeight) / 2;

  // 设置div的位置
  div.style.position = 'absolute';
  div.style.left = left + 'px';
  div.style.top = top + 'px';
}

// 调用函数以居中div
centerDiv();