When Words “go out the Window”

This has been bugging me for a while. I’m reading a book, sometimes published by a well-known publisher, when I come across a line like “he walked out the door” or “she looked out the window”.

What’s wrong with that? Well, I’m starting to doubt myself now and. Maybe nothing is wrong. But shouldn’t it be “he walked out of the door” or “she looked out of the window”?

I wondered if this was acceptable now or if it’s always been and I’ve never noticed it before (to cut out the word “of”) but when I asked in a Facebook writing group, everyone said it wasn’t. Yet it still happens, and I keep seeing this mistake everywhere; professionally published and edited books and recently in course materials. I can either assume everyone else is wrong and I’m right (unlikely?) or it’s okay and I should just let it go. If it’s a mistake like someone suggested, why is everyone making it?

I often end up shouting “Of, Of, Of” at whatever book I happen to be reading and it’s really ruining my enjoyment of the book. (Or enjoyment the book?) It makes me want to throw that book out (of) the window.

So, please comment and let me know what you think. Is cutting the word “of” out of a sentence, acceptable in books and other written material? Should I just go with it? Maybe I should just look out the window and count to ten, before carrying with the rest of the book.