window.onresize(当你改变窗口大小的时候会触发这个事件)
写法:
<script>
var body=(document.getElementsByTagName("body"))[0];
function beijing(){
var bjHeight=window.innerHeight,
bjWidth=bjHeight*(1920/1080),
windowWidth=window.innerWidth;
if( bjWidth<=windowWidth ){
body.style.backgroundSize=windowWidth+"px "+bjHeight+"px";
}else if( bjWidth>windowWidth ){
body.style.backgroundSize=bjWidth+"px "+bjHeight+"px";
}
}
beijing();
window.onresize=function(){
beijing();
}
</script>