$(document).ready equivalent without jQuery

I have a script that uses $(document).ready, but it doesn't use anything else from jQuery. I'd like to lighten it up by removing the jQuery dependency. How can I implement my own $(document).ready functionality without using jQuery? I know that using window.onload will not be the same, as window.onload fires after all images, frames, etc. have been loaded.

[tri-star]

jQueryなしでDomLoadedイベントを扱う場合。IE8を捨てられればある程度シンプルになりそう。

[masakielastic2]

ready に結びつけられているのは DOMContentLoaded イベント。