asyncadd.js

funnction asyncAdd(a,b,cb){
    try{
        cb(null,a+b);
    }except(e){
        cb(e);
    }
}

asyncAdd(2,5,function(err,success){
    if(err){
        console.log('oh noes!');
    }else{
        console.log(success);
    }
});