问检测滚动方向时出错

EN

var lastS=$(window).scrollTop();

function whatHappened()
{
    var currentS=$(window).scrollTop();
    console.log(lastS,currentS);

    if(currentS>lastS)
    {
       lastS = currentS;
       return "Scroll down";
    }
    else
    {
        lastS = currentS;
        return "Scroll up";
    }
}

$(window).on("mousewheel",function(){
    console.log(whatHappened());
});