尝试获取div的大小时出现错误

window.onload = function() {
  var divElement = document.getElementById('your-div-id');
  var divWidth = divElement.offsetWidth;
  var divHeight = divElement.offsetHeight;
  console.log('Div width: ' + divWidth + 'px');
  console.log('Div height: ' + divHeight + 'px');
};

var divElement = document.querySelector('.your-div-class');

.your-div-class {
  width: 100%;
  height: 200px;
  padding: 10px;
  margin: 20px;
  box-sizing: border-box;
}

// 示例使用Promise
function getContent() {
  return new Promise(function(resolve, reject) {
    // 异步获取内容的代码
    // ...
    if (contentLoaded) {
      resolve();
    } else {
      reject('Content loading failed');
    }
  });
}

getContent().then(function() {
  var divElement = document.getElementById('your-div-id');
  var divWidth = divElement.offsetWidth;
  var divHeight = divElement.offsetHeight;
  console.log('Div width: ' + divWidth + 'px');
  console.log('Div height: ' + divHeight + 'px');
}).catch(function(error) {
  console.error(error);
});