The principle and implementation of jquery's lazy loading

function isVisible($node){    var winH = $(window).height(),
        scrollTop = $(window).scrollTop(),
        offSetTop = $(window).offSet().top;    if (offSetTop < winH + scrollTop) {        return true;
    } else {        return false;
    }
}

$(window).on("scroll", function{    if (isVisible($node)){        console.log(true);
    }
})

var hasShowed = false;
$(window).on("sroll",function{    if (hasShowed) {        return;
    } else {        if (isVisible($node)) {
            hasShowed = !hasShowed;            console.log(true);            //ajax请求刷新view层
        }
    }
})