Lorenz Lo Sauer

我修改了这个简短的jquery函数扩展,您可以随意使用(mit license)。

/**
 * returns true if an element is visible, with decent performance
 * @param [scope] scope of the render-window instance; default: window
 * @returns {boolean}
 */
jQuery.fn.isOnScreen = function(scope){
    var element = this;
    if(!element){
        return;
    }
    var target = $(element);
    if(target.is(':visible') == false){
        return false;
    }
    scope = $(scope || window);
    var top = scope.scrollTop();
    var bot = top + scope.height();
    var elTop = target.offset().top;
    var elBot = elTop + target.height();

    return ((elBot <= bot) && (elTop >= top));
};