Question

Interating all fields in a form

Asked by: stefanlennerbrant

I'm using the following function to iterate through fields in a form.
However, I need to make sure it works both in IE and FireFox (and in other browsers)

I have succesfully used:

 var elements = document.myForm.elements;
 var length = elements.length;
 for(var loop = 0; loop < length; loop++)
  if(elements.item(loop).name=="test") alert('Test found');

However, it takes very very long time if there are many many fields in the form. I've identified that elements.item() is to blame

Now, I've changed it to
 var elements = document.myForm.elements;
 var length = elements.length;
 for(var loop = 0; loop < length; loop++)
  if(elements[loop].name=="test") alert('Test found');

This works much faster, but I've understood that it is not really the proper way to do things, as the use of elements[] implicitly uses the "all" collection that only works in Internet Explorer?
Or is this "only illegal" when doing it this way instead (I haven't really tried on FireFox yet):
 var length = document.myForm.elements.length;
 for(var loop = 0; loop < length; loop++)
  if(document.myForm.elements[loop].name=="test") alert('Test found');

So, the question in:
which is the proper (compatible) way of iterating through fields in a form. And still not pay the performance penalty that item() seems suffer from.


Another way of doing it, which makes me pussled, is the following:
 var elements = document.myForm.elements;
 for(var value in elements)
  if(value=="test") alert('Test found');

It works, but it iterates through a lot more than just the fields!
Apart from the field names themselves, values like "language, scrollHeight, isTextEdit, currentStyle" etc etc is looped through.
The "length" attribute of elements is however the same, such that the actual content of elements (seen by "for value in elements") is larger than the "length" attribute.
Why is this?

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Asked On
2008-08-28 at 05:41:32ID23685175
Tags

Iterate

,

form fields

,

compatibility

,

Internet Explorer

,

Firefox

Topics

JavaScript

,

Dynamic HTML (DHTML)

Participating Experts
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Comments
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Answers

 

by: MorcalavinPosted on 2008-08-28 at 07:27:12ID: 22335239

Using item[index] shouldn't be illegal.  It's only of the many ways you can reference your objects/collections, which are stored with key->value pairs.  The below code worked for me in all browsers I tested, assuming your form had an id of 'myform'.

As far as "for(i in ...){...}".  This iterates over all the keys(properties, methods, etc) in a particular object, in this case, the "elements" object/collection.

	var myform = document.getElementById('myform');
	var length = myform.length;
	for (var i = 0, e = length; i < e; i++)
	{
		if (myform[i].name === 'test')
		{
			alert('We found test!');
		}
	}

                                              
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by: nivlamPosted on 2008-08-28 at 07:28:25ID: 22335253

Are you just looking for fields with the name "test" ?  You could use document.getElementsByName() method if that's the case.

When you mean all "fields" in a form, are you talking about input fields?  How many "fields" are there in your form if it takes such a long time to loop through them all?

Something like this might work if they are inputs:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
	<script type="text/javascript">
	function go() {
		var inputs = document.getElementById('formMe').getElementsByTagName('input');
		
		for (var i = 0; i < inputs.length; ++i) {
			if (inputs[i].type == 'text')
				alert('hit');
		}
	}
	</script>
</head>
<body onload="javascript:go()">
	<form id="formMe">
		<input type="text" />
		<input type="text" />
		<input type="text" />
		
		<input type="button" />
		<input type="button" />
		<input type="button" />
	</form>
</body>
</html>

                                              
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by: stefanlennerbrantPosted on 2008-08-29 at 05:01:15ID: 22344468

I previously used:
for(var loop = 0; loop < length; loop++)
  if(document.myForm.elements[loop].name=="test") alert('Test found');

but changed to using item():
  if(document.myForm.elements.item(loop).name=="test") alert('Test found');

because Firefox had problems with the former one - as far as I understood, because the myForm.elements[] method assumed that "all" existed
(or maybe I used "document.myForm[loop].name" -- I don't remember now)

The item() method is very slow; with 1000 fields (as a test) it takes a few seconds to loop through the fields in InternetExplorer. FireFox seems to be quick even with item()

But if it's ok to use
  document.myForm.elements[loop].name
in all kinds of browsers, this is the solution. It seems to work in both IE and FF.
Thus, this is the question: Is it ok?

Also, intrestingly,
  for(var value in document.myForm.elements)
results in very different results in IE and in FF. Strange?

/Stefan

 

by: stefanlennerbrantPosted on 2008-08-29 at 05:12:01ID: 22344553

Ops, an update:

The problem in IE is not
elements = document.myForm.elements;
for(var loop = 0; loop < length; loop++)
  if(elements[loop].name=="test") alert('Test found');

Instead the severe performance penalty occurs in:
for(var loop = 0; loop < length; loop++)
  if(document.myForm.elements[loop].name=="test") alert('Test found');

Perhaps item() is not the real problem here at all, but rather accessing document.RegForm to get the elements list.

 

by: scrathcyboyPosted on 2008-08-29 at 19:01:01ID: 22350252

OK to start TOTALLy afresh here, every form element is nothing but part of an array.  Note carefully --

var first = document.form1.elements[0].value;
var second = document.form1.elements[1].value;
var third = document.form1.elements[2].value;
var fourth = document.form1.elements[3].value;
var fifth = document.form1.elements[4].value;

So you just initialize the COUNTER = 0 -- that is ALL you have to do, and then find the length of --
document.form1.elements.length

The fastest iteration of all is to use direct indexing, as I just did -  elements[x] where x = number.
If you have less than 10 form elements, itemize them one by one, it is faster.  If more, use the loop.

 

by: stefanlennerbrantPosted on 2009-12-27 at 14:15:48ID: 26128508

The problem here was that
  for(...)
    do_something_with( document.myForm.elements[i] )

was VERY slow in InternetExplorer.

When using
  var elements = document.myForm.elements;
  for(...)
    do_something_with( elements[i] )

it all ran VERY much faster.

So the case is closed. But not according to the suggestions above?
Please advice, EE moderators...

20120131-EE-VQP-002

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