版权声明： https://blog.csdn.net/qq_31255557/article/details/89842694
function average(){
var sum = 0;
for (var i=0;i<arguments.length;i++) {
sum = sum+arguments[i];
}
return (sum/arguments.length);
}
var aver = average(1,2,3,4,5,6);
alert(aver);