trance

var refreshTimer = null,
	mebook = mebook || {};

/*
*滾動(dòng)結(jié)束 屏幕靜止一秒后檢測哪些圖片出現(xiàn)在viewport中
*和PC端不同 由于無線速度限制 和手機(jī)運(yùn)算能力的差異 1秒鐘的延遲對(duì)手機(jī)端的用戶來說可以忍受
*/
$(window).on('scrollstop', function () {
	if (refreshTimer) {
		clearTimeout(refreshTimer);
		refreshTimer = null;
	}
	refreshTimer = setTimeout(refreshAll, 1e3);
});
	
	
$.belowthefold = function (element) {
    var fold = $(window).height() + $(window).scrollTop();
    return fold <= $(element).offset().top;
};

$.abovethetop = function (element) {
    var top = $(window).scrollTop();
    return top >= $(element).offset().top + $(element).height();
};

/*
*判斷元素是否出現(xiàn)在viewport中 依賴于上兩個(gè)擴(kuò)展方法 
*/
$.inViewport = function (element) {
    return !$.belowthefold(element) && !$.abovethetop(element)
};

mebook.getInViewportList = function () {
    var list = $('#bookList li'),
        ret = [];
    list.each(function (i) {
        var li = list.eq(i);
        if ($.inViewport(li)) {
            mebook.loadImg(li);
        }
    });
};

mebook.loadImg = function (li) {
    if (li.find('img[_src]').length) {
        var img = li.find('img[_src]'),
            src = img.attr('_src');
        img.attr('src', src).load(function () {
            img.removeAttr('_src');
        });
    }
};