关于一个自适应屏幕的高宽

function leftTop(obj){
var screenHeight = $(window).height();
console.log(screenHeight);
//var scrolltop = $(document).scrollTop();
var objTop = (screenHeight - 576)/2;
//console.log(objTop);
if(objTop<0){
objTop=0;
}
obj.css({ top: objTop + 'px'});
}
function center(obj) {
leftTop(obj);
//浏览器窗口大小改变时
$(window).resize(function() {
leftTop(obj);
});
}