Give a non-negative integer num, repeatedly adds the numbers in all positions until you get an one-digit integer.

<script>
    function getOne(num){
        var strArr=String(num).split("");
        var sum=strArr.reduce(function(init,item){
            init=init+Number(item);
            return init;
        },0);
        if(sum<10){
            return sum;
        }else{
            getOne(sum);
        }
    }
    console.log(getOne(343));
</script>

I would like to ask why the final printed result is undefined

Javascript
Sep.06,2021

A return is missing 

     function getOne(num){
        var strArr=String(num).split('');
        var sum=strArr.reduce(function(init,item){
            init=init+Number(item);
            return init;
        },0);
        if(sum<10){
            return sum;
        }else{
            return getOne(sum); // return
        }
    }
    console.log(getOne(343));

Why do you need to add return here?

suggest shorthand 

function getOne(num){ 
  var strArr=String(num).split(''); 
  var sum = strArr.reduce(function(init,item){ 
    return init+Number(item); 
  },0);
  return sum<10? sum : getOne(sum);
}

Previous: Ask how to use the scanf function. What happened to this program?

Next: Ask how to configure multiple vue projects with nginx

css mysql arrays josn react html typescript webpack npm sass R objective-c .net sql-server jquery python-3.x angularjs django angular excel regex iphone ajax linux xml pandas vba spring database wordpress string wpf xcode windows bash postgresql oracle multithreading eclipse list firebase algorithm macos forms image scala visual-studio azure bootstrap spring-boot react-native python-2.7 docker performance function winforms matlab powershell apache dataframe api sqlite numpy rest shell selenium flutter dart maven loops qt swing android-studio csv express file class tensorflow sorting codeigniter perl
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3e6bf-2c406.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3e6bf-2c406.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
Need Help?