这叫做onload。在DOM准备就绪之前，它已经出现了，并且实际上已经创建了DOM就绪，因为onload等待图像的确切原因。

That's called onload. It came waaaaay before DOM ready was around, and DOM ready was actually created for the exact reason that onload waited on images.

window.onload = function () { alert("It's loaded!") }