将对象格式的style转换为字符串格式

var style = {
    position:'absolute',
    background:'red',
    width:'2px',
    height:'2px',
    color:'#fff',
    top:x,
    left:y,
    'z-index':1e5
};

var s = [];
$.each(style,function(i,n){
    s.push(i+':'+n);
});
s = s.join(';')