js先按照age排序 age相同再按照top排序

Question

varobj=[{
id:1,
age:20,
top:5
},{
id:3,
age:21,
top:6
},{
id:2,
age:20,
top:8
}]
functionkeysort(property){
returnfunction(a,b){
varvalue1=a[property]=='-'?0:a[property];
varvalue2=b[property]=='-'?0:b[property];
returnvalue1-value2;
}
}
varobj1=obj.sort(keysort('age'));
写一半不会写了age相同的情况下再按照top从高到低排序想请教下老司机