Return array in function gives undefined javascript

Question

Little weird behaviour in my javascript. I want to make a document.ready cleaner by using functions that return manipulated arrays.

function manipulateArray(arrayToBeManipulated){
  var result=new Array();
  //...push something in result....
  result.push(arrayToBeManipulated[0]);
  console.log(result);
  return result;
}

The console.log always shows me the correct result. But when I invoke the method

//...code...//
var x=new Array();
//push something into x
var result=manipulateArray(x);
console.log(result);

It always shows me undefined. Is there a reason for this?

EDIT maybe I forgot to tell that the function is called inside a $.ajax request. Could this be the problem?

I see the expected result when I test it using [jsFiddle](http://jsfiddle.net/8s85u24m/). How do you get undefined? — Robin, Jun 02 '15 at 09:06
Does the second console log retur you `undefined` or `[undefined]` ? — Remy Grandin, Jun 02 '15 at 09:09

score 3 · Answer 1 · answered Jun 02 '15 at 09:07

3

The result of that is not undefined it is [undefined].

You create array X with nothing in it.
You create array Y with nothing in it.
You push the 0 index of array X (which is implicitly undefined) into Y
You return Y (which now has an explicit value of undefined for index 0.

answered Jun 02 '15 at 09:07

Quentin

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I skipped the part where I actually manipulate the array to see if there was anything wrong with the `return` itself – riciloma Jun 02 '15 at 09:29
@RiccardoLomazzi — You need to provide a test case that actually reproduces your problem. – Quentin Jun 02 '15 at 09:39

score 2 · Answer 2 · answered Jun 02 '15 at 09:08

That is because your new Array x is empty, push something into it because when you are manipulating the array in the function, you took the first index which is [undefined] for your problem,

I have pushed single element and it works now

function manipulateArray(arrayToBeManipulated){
  var result=new Array();
  //...push something in result....
  result.push(arrayToBeManipulated[0]);
  console.log(result);
  return result;
}


//...code...//
var x=new Array();
x.push(1);
var result=manipulateArray(x);
console.log(result);

I've edited the first post with a clarification about where the function is called — riciloma, Jun 02 '15 at 09:33

Return array in function gives undefined javascript

2 Answers2