jquery judge whether the scroll bar reaches the top or bottom

[size=medium]

var scroll_top = $(document).scrollTop(); //scroll_top is the height of the top of the scroll bar from the top of the document
var doc_height = $(document).height();//doc_height is the height of the document
var window_height = $(window).height();//window_height represents the height of the window

[/size]

When scroll_top = 0, the scroll bar has reached the top of the window.
When scroll_top + window_height >= doc_height, it means the scroll bar has reached the bottom of the window.

eg: Monitor in real time whether the scroll bar reaches the top

  

<script>
        $("document").ready(function () {
            ifTop();
            $(window).scroll(function () {
                ifTop();
            });
            function ifTop() {
                var scroll_top = $(document).scrollTop();
                if(scroll_top == 0){
                    console.log("Top.");
                }else {
                    console.log("Not to the top.");
                }
            }
        });
    </script>