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Question about arrays

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jmasta

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Question about arrays

Aug 18th, 2008

Hello everyone, I just have a quick Javascript question I haven't found an answer to on the net. What is the difference between
arrayName[0] and
arrayName.item(0) I've run across instances of both, but nowhere have I seen the difference between the two.
Thank you,
Jmasta

Last edited by jmasta; Aug 18th, 2008 at 1:50 pm.

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essential

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Re: Question about arrays

Aug 18th, 2008

Current best-practice eschews the "new" keyword on Javascript primitives. If you want to create a new Array simply use brackets [] like this...

var myArray = [];

You don't need to tell Javascript how many items to size the Array for. Javascript will automatically increase the size of the Array as needed, as you add items into the Array. Creating an Array with brackets instead of with the "new" constructor avoids a bit of confusion where you want to initialize only one integer. For instance.

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 JavaScript / DHTML / AJAX Syntax (Toggle Plain Text) 
var badArray = new Array(10); // Creates an empty Array that's sized for 10 elements.
 
 
var goodArray= [10];      // Creates an Array with 10 as the first element.
var badArray = new Array(10); // Creates an empty Array that's sized for 10 elements.


var goodArray= [10];      // Creates an Array with 10 as the first element.

As you can see these two lines do two very different things. If you had wanted to add more than one item then badArray would be initialized correctly since Javascript would then be smart enough to know that you were initializing the array instead of stating how many elements you wanted to add.
Since the new constructor is not necessary with Arrays and there's a slight chance of unintended results by using the new constructor, it's recommended you not use "new Array()" to create an Array.

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Re: Question about arrays

Aug 18th, 2008

Usually when you see something like this:
arrayName.item(0)

it is referring to something in the DOM, for example:
http://jacksleight.com/blog/2008/01/14/getelementsby/

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jmasta

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Re: Question about arrays

Aug 19th, 2008

I'm sorry, I should have been more clear. Let's say I already did something like
var pageInputs = getElemetsByTagName("input"); Now, i have a collection, pageInputs. So what's the difference between
console.log(pageInputs[0]) and
console.log(pageInputs.item(0))
I haven't had a chance to test them, but wouldn't they return the same thing? I just hadn't seen the '.item()' syntax before.

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langsor

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Re: Question about arrays

Aug 19th, 2008

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Originally Posted by R0bb0b

Usually when you see something like this:
arrayName.item(0)

it is referring to something in the DOM, for example:
http://jacksleight.com/blog/2008/01/14/getelementsby/

R0bb0b is correct ... item(0) accesses a node-collection

 Help with Code Tags 
 JavaScript / DHTML / AJAX Syntax (Toggle Plain Text) 
<script type="text/javascript">
 
arr = [];
arr[0] = 'one';
arr['two'] = 3;
 
alert( arr[0] );
alert( arr['two'] );
 
$links = document.getElementsByTagName('a');
for ( var i = 0; i < links.length; i ++ ) {
  alert( links.item(i).href );
}
</script>
<script type="text/javascript">

arr = [];
arr[0] = 'one';
arr['two'] = 3;

alert( arr[0] );
alert( arr['two'] );

$links = document.getElementsByTagName('a');
for ( var i = 0; i < links.length; i ++ ) {
  alert( links.item(i).href );
}
</script>

as an example of different arrays / node collections

Last edited by langsor; Aug 19th, 2008 at 1:46 am.

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Re: Question about arrays

Aug 19th, 2008

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Originally Posted by jmasta

I'm sorry, I should have been more clear. Let's say I already did something like
var pageInputs = getElemetsByTagName("input"); Now, i have a collection, pageInputs. So what's the difference between
console.log(pageInputs[0]) and
console.log(pageInputs.item(0))
I haven't had a chance to test them, but wouldn't they return the same thing? I just hadn't seen the '.item()' syntax before.

Yes, they would return the same thing and are effectively the same, but the .item(0) is the correct syntax for DOM node-collections, but the array access syntax is cross-browser supported.

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