Proper syntax to return variable and use it again (javascript)

Question

I have this very simple thing, that doesn't work. What is happening? According to the tutorials that I have read, this should output 4...

function sum(a,b) {
    var result = a + b;
    return result;
    }

sum(2,2);        
var test = sum();

alert(test); // shouldn't this return "4"?

Link to the JSFiddle

sum(2,2) executes the function. var test = sum() assigns the result of sum without parameters, of course NaN. — elclanrs
– elclanrs, Commented Nov 7, 2012 at 0:06
sum(2,2) does return 4, sum() alone does return NaN - what did you expect (or: which tutorials did you read)? — Bergi
– Bergi, Commented Nov 7, 2012 at 0:06
I expected that var test = sum() would not run the function. Instead it would just retrieve the returned value. But then again, I have been studying javascript (and programming in general) mere few weeks. — telex-wap
– telex-wap, Commented Nov 7, 2012 at 0:14

Korikulum · Accepted Answer · 2012-11-07 00:05:56Z

2

function sum(a,b) {
    var result = a + b;
    return result;
}

var test = sum(2,2);

alert(test);

answered Nov 7, 2012 at 0:05

Korikulum

2,62923 silver badges26 bronze badges

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

Comments

Spencer Ruport · Accepted Answer · 2012-11-07 00:06:11Z

1

Change this:

sum(2,2);        
var test = sum();

To this:

var test = sum(2,2);

The first code isn't technically wrong it just isn't doing what you're trying to do. You're calling the sum function with the appropriate values but never setting it's return value to any variable so it just gets thrown away. You seem to be under the impression that the value will "stick" to the function and this isn't the case. (Some BASIC languages can make it seem this way though. Perhaps that's where your misconception is coming from.)

Your second call is essentially the equivalent of

var test = sum(null, null);

and when you concatenate two null values you get null again.

answered Nov 7, 2012 at 0:06

Spencer Ruport

35.2k12 gold badges89 silver badges150 bronze badges

7 Comments

Bergi Over a year ago

No. undefined is not null, and both return NaN when summing them instead of null.

telex-wap Over a year ago

I realized that it looked strange to call the function without parameters, but... my very limited experience has shown me that when you do that: var test = sum(2,2) the function RUNS again, and I didn't want it to run, I just wanted to retrieve the value. That's why I was a bit confused.

Spencer Ruport Over a year ago

@Bergi - I didn't feel like throwing a bunch of new terms at him.

Spencer Ruport Over a year ago

@telex-wap - The function will run every time you call it. Functions have no inherent way of storing past values. That's what variables are for. :)

telex-wap Over a year ago

Yes, the only problem being, that if you store the returned value in a variable inside the function, you cannot use it outside... (or at least you cannot in the beginner level where I am. I guess there must be a way to get around that easily)

|

Collectives™ on Stack Overflow

Proper syntax to return variable and use it again (javascript)

2 Answers 2

Comments

7 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

7 Comments

Your Answer

Sign up or log in

Post as a guest

Related