Arrays not truly passed by reference in functions

Aman Sura · #1 August 2nd, 2006, 08:35 AM

:confused: This is just an absurd piece of code. Can anyone please explain the reason?

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//a function that nulls the array passed as parameter

function Nullify(arrRef)

{

 arrRef = null;

}
 
var arr = new Array();

for(var i = 0; i < 5; i++)

  arr[arr.length] = "myString" + i;
 
alert("Length Before : " + arr.length); //This gives 5 as expected
 
Nullify(arr);  //this should null the array
 
alert("Length After : " + arr.length); //STRANGE : This also gives 5. Should it not give a javascript error?

According to the above code, it seems that array "arr" is not passed by reference. However if i splice( ) 2 elements in the function Nullify( ), then that alert message gives 3. ???

iam_clint · #2 August 2nd, 2006, 06:29 PM

I see your problem take a close look and you will to

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function Nullify(arrRef)

{

 arrRef = null; // Assuming you are trying to nullify the var arr, Well you cannot do it this way you cannot use a variable as another variable get what i mean arrRef is not gonn reference to arr.

}

so this would be the way to fix it

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<script>

function Nullify()

{

 arr = '';

}
 
var arr = new Array();

for(var i = 0; i < 5; i++)

  arr[arr.length] = "myString" + i;
 
alert("Length Before : " + arr.length); //This gives 5 as expected
 
Nullify();  //this should null the array
 
alert("Length After : " + arr.length); //STRANGE : This also gives 5. Should it not give a javascript error?

</script>

Aman Sura · #3 August 3rd, 2006, 04:58 AM

Thanks for the reply clint.

As you said

Quote:

Well you cannot do it this way you cannot use a variable as another variable get what i mean arrRef is not gonn reference to arr

But I am passing "arr" as a parameter in the function Nullify. So inside the function should not arr and arrRef point to same thing?
Instead of doing

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arrRef = null

If i do any other changes, for instance I use splice( ) method to delete an element from arrRef.

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arrRef.splice(0,1)

These changes are reflected pretty fine, when I come out of the function Nulllify. The alert message gives the length of array as 4 now, which is what it should be.
Only arrRef = null does not work. Apart from this any changes in arrRef are reflected in arr.

I hope i made myself clear.

iam_clint · #4 August 3rd, 2006, 09:47 PM

Yes and no take a look what the script you are trying does

ok so your calling the function nullify with the parameter of arr
and you got function nullify(arrRef)
so it sets arr to arrRef -- two completely separate variables

so now arrRef is an array and aar is an Array
think of it this way
arr = "a";
arrRef = arr;

now arr and arrRef both = a

down the line if i put arrRef = null;

alright so arrRef is null now but arr is still a.

iam_clint · #5 August 3rd, 2006, 09:52 PM

If that didn't clarify my point try this script with the alerts in there.

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<script>

//a function that nulls the array passed as parameter

function Nullify(arrRef)

{

alert("arrRef = " + arrRef);

alert("arr = " + arr);

arrRef = null;

alert("arrRef = " + arrRef);

alert("arr = " + arr);

}

var arr = new Array();

for(var i = 0; i < 5; i++)

  arr[arr.length] = "myString" + i;
 
Nullify(arr);  //this should null the array
 
</script>

Aman Sura · #6 August 4th, 2006, 07:02 AM

Ok thanks dear. Got the point.

Arrays not truly passed by reference in functions

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