Facebook如何知道您何时停止在文章/图片中

Question

First of all, I don't know if this is the right place to post this question. If it is, I'm sorry.

Everytime you go through facebook newsfeed you stop at some image to look at it or an article that you found interesting but didn't click on it . If you go to some page and come back to the newsfeed you will likely see the same image on the top of your newsfeed .

I tried to look for some function/algorithm but didn't find any.

Others website doesn't have such feature eg Quora and mySpace .

My question here is: How does Facebook knows that you stopped to look at that picture/article? if such function exists or it's only my stupid mind playing tricks on me.

Answer 1

I guess facebook detect your scroll position.

Every website can run a script that detect your scroll position every second, and then know if you're stopped (stay on the same position or same range of pixels for a while) in a post, picture or a video. Then you can decide if the user find the content interesting or not.

It's simple with jQuery:

var s = $('body').scrollTop();