浏览器 导航性能 loadEventEnd 指标可用于确定是否触发了加载事件:

Browser navigation performance loadEventEnd metric can be used to determinate if load event was triggered:

let navData = window.performance.getEntriesByType("navigation");
if (navData.length > 0 && navData[0].loadEventEnd > 0)
{
    console.log('Document is loaded');
} else {
    console.log('Document is not loaded');
}