您将希望向if语句中添加条件以将其打开或关闭，如下所示:

You will want to add a condition to your if statement to turn it up or down like so:

if(delta== 1 && popo.volume <= 0.9){popo.volume+=0.1;}
if(delta== -1 && popo.volume > 0.1){popo.volume-=0.1;}

演示