Javascript - Why sometimes it is "undefined" when using return?

Question

The codes below works:

var myArray = [];
function myFunc(){
    var randomNumber = Math.floor(Math.random() * 4);
    if(myArray.indexOf(randomNumber) == -1){
        myArray.push(randomNumber);
        console.log(randomNumber); //; didn't use return
    } else {
        myFunc();
    }
}
for(let i=0; i<4; i++){
    myFunc();
}

While the following doesn't, both are almost the same except the following is using "return".

var myArray = [];
function myFunc(){
    var randomNumber = Math.floor(Math.random() * 4);
    if(myArray.indexOf(randomNumber) == -1){
        myArray.push(randomNumber);
        return randomNumber; // using return
    } else {
        myFunc();
    }
}
for(let i=0; i<4; i++){
    console.log(myFunc());
}

The results may not be the same as those are random numbers, please try to refresh it for several times.

I want to use return so that the value could save into the function.

Thanks everyone.

Yachay J. Tolosa · Accepted Answer · 2017-10-23 03:18:42Z

2

It returns undefined because you are not returning anything when myArray.indexOf(randomNumber) != -1. Try:

function myFunc(){
    var randomNumber = Math.floor(Math.random() * 4);
    if(myArray.indexOf(randomNumber) == -1){
        myArray.push(randomNumber);
        return randomNumber; // using return
    } else {
        return myFunc();
    }
}

answered Oct 23, 2017 at 3:18

Yachay J. Tolosa

1446 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Kenny Over a year ago

Thank you very very much Yachay. In the else clause, I just want to run the function again if certain condition is matched. Do you mind to tell me why should I use "return myFunc()" instead of just running the function again? Thanks again

Yachay J. Tolosa Over a year ago

Because, otherwise, when you call "myFunc" again the returned value is lost.

Kenny Over a year ago

Thank you very much Yachay! Have a nice day.

Collectives™ on Stack Overflow

Javascript - Why sometimes it is "undefined" when using return?

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related