话不多说，请看代码
1650){
document.getElementById ('msg').value ='窗口大小：' + 'width:' + w;
bgImg = document.getElementById('bg').getElementsByTagName('img')[0];
bgImg.width = (w - 5);
}else{
document.getElementById ('msg').value ='窗口大小：' + 'width:' + w;
bgImg = document.getElementById('bg').getElementsByTagName('img')[0];
bgImg.width = 1650;
}
}
