判斷元素是否在螢幕可視範圍內.js

function isScrolledIntoView(elem) {
    var docViewTop = $(window).scrollTop();
    var docViewBottom = docViewTop + $(window).height();

    var elemTop = $(elem).offset().top;
    var elemBottom = elemTop + $(elem).height();

    return (elemTop <= docViewBottom) && (elemBottom >= docViewTop);
}