What are reasons to use return as a function in JavaScript?

Question

while I was going through concepts related to JavaScript functions, I came up with problem which I'm unable to figure it out. I use following codes i.e one with return as a function and the other as a simple function as follows

function plus(a, b) {
   return(
       console.log(a+b),
       console.log(this),
       console.log(arguments)
   )
}
plus(4,5);

and

function plus(a, b) {      
       console.log(a+b),
       console.log(this),
       console.log(arguments)
}
plus(4,5)

But when I run both I'm not able to figure it out since both results same in console. So I just want to know when should I use return as function.? and what is its main purpose? I've seen answers here but those related to return entire function or objects but didn't find specific answer to return as a function. So please help me in it.

You don't return a function here, you return undefined in both cases. — zerkms
– zerkms, Commented Jan 16, 2015 at 1:08
@zerkms That's return "as a function" not "return a function", by which the OP must mean calling return with a () enclosed list of statements. — Michael Berkowski
– Michael Berkowski, Commented Jan 16, 2015 at 1:10

zerkms · Accepted Answer · 2015-01-16 01:17:25Z

5

return(
       console.log(a+b),
       console.log(this),
       console.log(arguments)
   )

statement means:

return the argument that is represented by (...) expression. Here parentheses is not a part of a return keyword syntax, but is a standalone operator used in conjunction with operator ,.

The (1, 2, 3) expression after evaluating returns the value of the last expression.

In your case it's console.log(arguments) which returns undefined.

References:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comma_Operator

edited Jan 16, 2015 at 1:17

answered Jan 16, 2015 at 1:12

zerkms

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9 Comments

StackSlave Over a year ago

Would arguments not be the arguments Array-like Object?

zerkms Over a year ago

@PHPglue not sure what you mean

StackSlave Over a year ago

You say it's undefined when it would be a and b in an Array-like Object.

Kishore Kumar Korada Over a year ago

@zerkms how console.log(arguments) undefined when it gives array as PHPglue mentioned?

zerkms Over a year ago

@PHPglue: console.log call returns undefined

|

c-smile · Accepted Answer · 2015-01-16 04:23:12Z

1

This

function plus(a, b) {
   return(
       console.log(a+b),
       console.log(this),
       console.log(arguments)
   )
}

is an equivalent of this:

function plus(a, b) {
   var r = (
       console.log(a+b),
       console.log(this),
       console.log(arguments)
   );
   return r; 
}

or simply this (EDIT, but is wrong, see zerkms comment ):

function plus(a, b) {
   var r = 
       console.log(a+b),
       console.log(this),
       console.log(arguments);
   return r; 
}

where ,, is an expression - compute all parts delimited by commas with result of last expression.

edited Jan 16, 2015 at 4:23

answered Jan 16, 2015 at 1:18

c-smile

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1 Comment

zerkms Over a year ago

"or simply this:" --- unless it's syntactically incorrect.

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