DOM initialisation in IE 6

abcd_68 · Jan 12, 2006

All,

First off please note that I'm a novice at Javascript so please bear
with me.
Second, I did look at FAQs, this group, the web etc. but I'm still
stuck.

Problem is the following. I've got a fairly complex (for my abilities
at least) page with nested tables. Think of it as a small spreadsheet,
in which I have to perform computations (in Javascript of course) on a
per row basis and compute the grand totals in the bottom line. All the
rows are contained in a big form the will eventually be submitted. Upon
page loading I need to fill up arrays of references to the various
input elements so as to be able to quickly recompute totals in the
bottom line when the user changes some value. I do so by exploiting the
DOM, using constructs such as document.getElementById(), childNodes,
parent, etc.

So far so good and, as a matter of the fact, everything works perfectly
under firefox 1.5. Not so under IE 6 (on the same machine, running
WinXP SP2). Problem lies in the array initialisation. At first I used a
simple onload() function which works just fine under FF. This was not
working on IE so I set up an init() function (changed names just in
case, but the automatic association between event name and function
name does not seem to work under IE anyway) and tried all of the
following (one at a time of course):
<body onload=init>
window.onload = function () {init();}
window.onload = init
window.addEventListener('load', init, true|false)
window.attachEvent('onload', init)

Apart from addEventListener which IE frowns upon (I knew it wouldn't
work but I tried out of desperation), all the others "work" i.e., the
init function is actually called (my debugging alerts pop up). Problem
is, in all cases (under IE) said function fails to properly initialise
the arrays, issuing errors such as "childNodes is null or not an
object" and the like.

In my (possibly naive) interpretation, the root of the problem is that
when init() is called the DOM hasn't been properly initialised yet. I
try to retrieve elements by id but those elements are not completely
formed e.g., they have no children. However, this is against all that I
read about onload being fired *after* everything has been properly set
up. And again, everything is working just fine under FF so the object
references I use do make sense.

I'm stuck... Can you help?

Thanks a lot,
Andy

RobG · Jan 13, 2006

Problem is the following. I've got a fairly complex (for my abilities
at least) page with nested tables. Think of it as a small spreadsheet,
in which I have to perform computations (in Javascript of course) on a
per row basis and compute the grand totals in the bottom line. All the
rows are contained in a big form the will eventually be submitted. Upon
page loading I need to fill up arrays of references to the various
input elements so as to be able to quickly recompute totals in the
bottom line when the user changes some value. I do so by exploiting the
DOM, using constructs such as document.getElementById(), childNodes,
parent, etc.

So far so good and, as a matter of the fact, everything works perfectly
under firefox 1.5. Not so under IE 6 (on the same machine, running
WinXP SP2). Problem lies in the array initialisation. At first I used a
simple onload() function which works just fine under FF. This was not
working on IE so I set up an init() function (changed names just in
case, but the automatic association between event name and function
name does not seem to work under IE anyway) and tried all of the

There is nothing that says a function called 'init' will be called by
window.onload simply because it exists and is called 'init'. You have
to assign either a reference or function to the window onload property,
the name is irrelevant (provided it meets the criteria for JavaScript
function names).

following (one at a time of course):
<body onload=init>

---------------^^^^^
Probably just a posting typo:

window.onload = function () {init();}
window.onload = init
window.addEventListener('load', init, true|false)
window.attachEvent('onload', init)

Apart from addEventListener which IE frowns upon (I knew it wouldn't
work but I tried out of desperation), all the others "work" i.e., the
init function is actually called (my debugging alerts pop up). Problem
is, in all cases (under IE) said function fails to properly initialise
the arrays, issuing errors such as "childNodes is null or not an
object" and the like.

In my (possibly naive) interpretation, the root of the problem is that
when init() is called the DOM hasn't been properly initialised yet. I

Or you are doing something that prevents IE from seeing the childNodes
but not Firefox. A recent issue was that using innerHTML on the title
element caused similar behaviour (but that may not be your problem).

AFAIK, onload works as expected in IE.

try to retrieve elements by id but those elements are not completely
formed e.g., they have no children. However, this is against all that I
read about onload being fired *after* everything has been properly set
up. And again, everything is working just fine under FF so the object
references I use do make sense.

I'm stuck... Can you help?

Post a URL or a minimal example that displays the behaviour.

abcd_68 · Jan 13, 2006

Hi Rob,

thanks for your reply.

There is nothing that says a function called 'init' will be called by
window.onload simply because it exists and is called 'init'.

True, if the function is called 'init'. Apparently not so if it bears
the name of an event, as documented in the Javascript bible 5th edition
(the only Javascript book I have at hand, don't know how reliable it
is), on page 168: "[...] you can define the action of an event handler
by defining a function with the event handler's name." Which does work
under FF.

Post a URL or a minimal example that displays the behaviour.

I can't post a URL due to the usual copyright stuff, I'll try to
isolate a minimal example.

Thanks

RobG · Jan 13, 2006

Hi Rob,

thanks for your reply.

There is nothing that says a function called 'init' will be called by
window.onload simply because it exists and is called 'init'.

Click to expand...

True, if the function is called 'init'. Apparently not so if it bears
the name of an event, as documented in the Javascript bible 5th edition
(the only Javascript book I have at hand, don't know how reliable it
is), on page 168: "[...] you can define the action of an event handler
by defining a function with the event handler's name." Which does work
under FF.

Yes, it 'works'. Danny Goodman's book is not held in high regard,
search the archives.

I haven't read the book - if you mean assigning a function to the value
of the window object's onload property using:

function onload(){alert('hey');}

there may well be technical reasons why that is never done. I've never
seen it and don't have the knowledge to know if it's good or bad. But I
suspect that the following are much more acceptable (as well as being
far more common) for a reason:

window.onload = funcRef;

or

window.onload = function(){
// function body
}

There are a couple of reasons for using window.onload rather than just
onload:

1. The lookup is faster (imperceptibly, but it all counts);
2. There is no doubt about the scope of the function, it
is unequivocally attached to the window object so better
maintenance.

The use of addEventListener/attachEvent is considered best of all. It
should be used if there is any doubt whether there might already be a
function assigned to window.onload (e.g. if a function within a script
library wants to attach a function to onload) - you can add/remove
functions without affecting others that might be attached.

[...]

Thomas 'PointedEars' Lahn · Jan 13, 2006

RobG said:
[...] if you mean assigning a function to the value
of the window object's onload property using:

function onload(){alert('hey');}

there may well be technical reasons why that is never done. I've never
seen it and don't have the knowledge to know if it's good or bad.

I think it is bad for it assumes that the Global Object is the object
referred to by `window' and that variable instantiation will allow for
replacing a property of that _host_ object. See ES3, sections 10.1.3,
pt. 2 and 10.2.1.

PointedEars

abcd_68 · Jan 13, 2006

Hi,

I finally solved the problem. It had nothing to do with DOM
initialisation at all. All the onload/setEventHandler/etc. stuff works
ok. The problem (predictably) was an error on my part.

Apparently IE and FF treat a table's children differently. Under IE the
firstChild of a table is the first row, whereas under FF it's something
else (maybe a a text node). So what happened was that one browser
needed a firstChild, while the other required childNodes[1].

I fixed the problem using:
var feeTable = document.getElementById('feeTable');
var rows = feeTable.rows; //instead of firstChild etc.
which works ok under both. This was probably obvious to all of you in
this ng but as I said I'm a Javascript novice.

Thanks a lot
Andy

RobG · Jan 13, 2006

Hi,

I finally solved the problem. It had nothing to do with DOM
initialisation at all. All the onload/setEventHandler/etc. stuff works
ok. The problem (predictably) was an error on my part.

Apparently IE and FF treat a table's children differently. Under IE the
firstChild of a table is the first row, whereas under FF it's something
else (maybe a a text node). So what happened was that one browser
needed a firstChild, while the other required childNodes[1].

The firstchild of a table is never a TR, it is always either a CAPTION, COL
or COLGROUP, THEAD, TFOOT or TBODY.

A tbody must always be present, it will be added by the browser if you don't.

I fixed the problem using:
var feeTable = document.getElementById('feeTable');
var rows = feeTable.rows; //instead of firstChild etc.
which works ok under both. This was probably obvious to all of you in
this ng but as I said I'm a Javascript novice.

It's actually a consequence of your HTML, you discovered it because of how
you were trying to access elements by traversing the DOM tree. Firefox
will insert text nodes where there is whitespace between elements[1], IE
generally doesn't. For example given the HTML:

<tr>
<td> ... </td>
</tr>

In Firefox the TR will have three child nodes, #text, TD then #text. In IE,
it will have just one - the TD. If the HTML was:

<tr><td> ... </td></tr>

both browsers will give the TR just one child - the TD. Using the rows
collection is much better.

Be aware that there might be browsers that don't support the rows
collection, there is at least one reasonably modern browser (Safari 1.0.3 -
Mac OS 10.2.8) that only partially supports the row cells collection (fixed
in later versions). There are a number of mobile browsers that seem to
have very patchy W3C DOM support (even though they may be well be fully
compliant with JavaScript 1.5).

You could perhaps use getElementsByTagName or walk down the DOM tree
testing nodeName, tagName or nodeType.

1. "Between" being either:

- after the opening tag of an element and before the
opening tag of a child node,

- after the closing tag of an element and before
the opening tag of a sibling, or

- after the closing tag of an element and before the
closing tag of its parent element.

Use the Firefox DOM inspector to see where they are, there will be other
#text nodes amongst element contents.

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DOM initialisation in IE 6

abcd_68

RobG

abcd_68

RobG

Thomas 'PointedEars' Lahn

abcd_68

RobG

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