Object referencing

[DoomedLung]

Hey everyone,

I'm currently reading Sitepoint's 'Javascript Anthology' and keep
spotting a reference I'm not quite familiar with, such as
'document.getElementByTagName('p')[0]'. What I want to know is if this
reference points to the first element with the containing object?

Cheers

[Noah Sussman]

On Mar 29, 11:21 am, "DoomedLung" <[e-mail]:

Hey everyone,

I'm currently reading Sitepoint's 'Javascript Anthology' and keep
spotting a reference I'm not quite familiar with,
such as
'document.getElementByTagName('p')[0]'.

What is happening here is that you are creating an array, and
dereferencing the array, both on the same line.
document.getElementsByTagName('p') gets an array (actually its a
NodeList, but just think of it as an array).
And document.getElementsByTagName('p')[0] gets the first item from
that array.

//bar gets the first P tag in the document
var bar = document.getElementsByTagName('p')[0];

is shorthand for

//foo gets a list of all the P tags in the document
var foo = document.getElementsByTagName('p');
//bar gets the first P tag from that list
var bar = foo[0];

[DoomedLung]

On Mar 29, 4:46 pm, "Noah Sussman" <[e-mail]:

On Mar 29, 11:21 am, "DoomedLung" <[e-mail]:

Hey everyone,

I'm currently reading Sitepoint's 'Javascript Anthology' and keep
spotting a reference I'm not quite familiar with,
such as
'document.getElementByTagName('p')[0]'.

What is happening here is that you are creating an array, and
dereferencing the array, both on the same line.
document.getElementsByTagName('p') gets an array (actually its a
NodeList, but just think of it as an array).
And document.getElementsByTagName('p')[0] gets the first item from
that array.

//bar gets the first P tag in the document
var bar = document.getElementsByTagName('p')[0];

is shorthand for

//foo gets a list of all the P tags in the document
var foo = document.getElementsByTagName('p');
//bar gets the first P tag from that list
var bar = foo[0];

I thought as much. Just needed to clear it up.

Cheers dude :)

[scripts.contact]

On Mar 29, 9:46 am, "Noah Sussman" <[e-mail]:

'document.getElementByTagName('p')[0]'.

What is happening here is that you are creating an array, and
dereferencing the array, both on the same line.
document.getElementsByTagName('p') gets an array

It's not array, it's a collection.

[Richard Cornford]

scripts.contact wrote:

On Mar 29, 9:46 am, Noah Sussman wrote:

>>'document.getElementByTagName('p')[0]'.

What is happening here is that you are creating an
array, and dereferencing the array, both on the same
line. document.getElementsByTagName('p') gets an array

It's not array, it's a collection.

The object returned from - getelementsByTagName - is a - NodeList
- not a collection. In a class-less language like ECMAScript being
a - NodeList - is just a matter of having the specified properties,
methods and characteristics of a - NodeList -, and as a result all
objects implementing the - HTMLCollection - interface are also
implementing the - NodeList - interface (so are NodeLists). But
NodeLists are not necessarily also HTMLCollections, and it would
be dangerous to assume that the objects returend from calls to
- getElementsById - have properties beyond those specified.

In class-based terminology it may be said that - HTMLCollection
- extends - NodeList, and actual examples may be implemented in
that way. In such a context it would be possible to case an -
HTMLCollection - into a - NodeList -, but not the other way around.

Richard.