阻止pgup使滚动条滚动

 pgup阻止默认行为（页面滚动条滚动）必须在keydown 中设置，keyup中是无效

$(document).keydown(function(event){

        console.log(event.keyCode);

        if (event.keyCode == 33){

             event.preventDefault();

             console.log(event.keyCode);

        }

        console.log("bbb")

    })