Check if radio button is checked

V

Vancouver

Hi there,

I have 24 radio button groups, and 7 options for each group. I wrote
code below trying to see if each radio button group is checked. But it
does not work. Any help? Thanks.

(24 radio button groups are named question[0] to question[23].
choices[] is to store true/false)

<script type="text/JavaScript">
function ifChecked()
{
var choices=new Array();

for (index=0;index<24;index++)
{
choices[index]=false;
for (i=0;i<7;i++)
{
if (document.forms[0].question[index].checked)
{
choices[index]=true;
break;
}

}
}
for (index=0;index<24;index++)
{
if (!choices[index])
{
alert ("Please make a selection");
return false;
}
}
return true;
}
</script>
 
V

Vancouver

Hi there,

I have 24 radio button groups, and 7 options for each group. I wrote
code below trying to see if each radio button group is checked. But it
does not work. Any help? Thanks.

(24 radio button groups are named question[0] to question[23].
choices[] is to store true/false)

<script type="text/JavaScript">
function ifChecked()
{
var choices=new Array();

for (index=0;index<24;index++)
{
choices[index]=false;
for (i=0;i<7;i++)
{
if (document.forms[0].question[index].checked)
{
choices[index]=true;
break;
}

}
}
for (index=0;index<24;index++)
{
if (!choices[index])
{
alert ("Please make a selection");
return false;
}
}
return true;}

</script>
Click to expand...


I managed to know why:

instead of if (document.forms[0].question[index].checked)
I need to a line like this: var name="question["+index+"]["+i+"]";,
and then: if (document.form1.name.checked)

But why? (Otherwise I get a null object) Why I cannot call
ocument.forms[0].question[index].checked directly?

Thanks
 
V

Vancouver

Hi there,
Click to expand...
I have 24 radio button groups, and 7 options for each group. I wrote
code below trying to see if each radio button group is checked. But it
does not work. Any help? Thanks.
Click to expand...
(24 radio button groups are named question[0] to question[23].
choices[] is to store true/false)
Click to expand...
<script type="text/JavaScript">
function ifChecked()
{
var choices=new Array();
Click to expand...
for (index=0;index<24;index++)
{
choices[index]=false;
for (i=0;i<7;i++)
{
if (document.forms[0].question[index].checked)
{
choices[index]=true;
break;
}
Click to expand...

}
}
for (index=0;index<24;index++)
{
if (!choices[index])
{
alert ("Please make a selection");
return false;
}
}
return true;}
Click to expand...
</script>
Click to expand...

I managed to know why:

instead of if (document.forms[0].question[index].checked)
I need to a line like this: var name="question["+index+"]["+i+"]";,
and then: if (document.form1.name.checked)

But why? (Otherwise I get a null object) Why I cannot call
ocument.forms[0].question[index].checked directly?

Thanks
Click to expand...


Too bad. I had thought I fixed the issue but it turns out I am wrong.
I still cannot make it work. Any help is highly appreciated.

Thanks,
 
H

Henry

On Mar 12, 4:03 am, Vancouver wrote:
if (document.forms[0].question[index].checked)
Click to expand...
Click to expand...

I managed to know why:

instead of if (document.forms[0].question[index].checked)
I need to a line like this: var name="question["+index+"]["+i+"]";,
and then: if (document.form1.name.checked)
Click to expand...


That will not work. There is no substitution of the contents of a
variable named 'name' for the Identifier 'name' used in a property
accessor. In practice you want to use a bracket notation property
accessor here, such as:-

document.forms[0].elements[("question["+index+"]")].checked

See:-

But why? (Otherwise I get a null object) Why I cannot call
document.forms[0].question[index].checked directly?
Click to expand...


You can, it just does not mean anything sensible in relation to what
you are doing.

Once you understand the role of square brackets in javascript syntax
you should see how it would be impractical to allow them to also be
part of an Identifier.
 
V

Vancouver

On Mar 12, 4:03 am, Vancouver wrote:
if (document.forms[0].question[index].checked)
Click to expand...
Click to expand...

I managed to know why:
Click to expand...
instead of if (document.forms[0].question[index].checked)
I need to a line like this: var name="question["+index+"]["+i+"]";,
and then: if (document.form1.name.checked)
Click to expand...


That will not work. There is no substitution of the contents of a
variable named 'name' for the Identifier 'name' used in a property
accessor. In practice you want to use a bracket notation property
accessor here, such as:-

document.forms[0].elements[("question["+index+"]")].checked

See:-

But why? (Otherwise I get a null object) Why I cannot call
document.forms[0].question[index].checked directly?
Click to expand...


You can, it just does not mean anything sensible in relation to what
you are doing.

Once you understand the role of square brackets in javascript syntax
you should see how it would be impractical to allow them to also be
part of an Identifier.
Click to expand...


Thanks Henry.

I am confused. In another page, I have a radio group named myUnique
and I use this to see if it is checked:

<script type="text/JavaScript">
function ifChecked()
{
for (i=0;i<document.form1.myUnique.length;i++)
{
if (document.form1.myUnique.checked)
return true;
}
alert ("Please make a selection");
return false;
}
</script>

It works.

I do not understand why similar code does not work in a multiple radio
groups page.

The only difference is that in the myUnique page, I just have one
radio group; in the other page, I have 24 groups, question[0] to
question[23].

Isn't document.FORM.RADIO_GROUP_NAME an identifier for this radio
group? I think I shall be able to traverse all options by
document.FORM.RADIO_GROUP_NAME.[index] (index=1 to the length of the
radio group)

Thank you,
 
H

Henry

On Mar 12, 5:20 am, Henry wrote:
Click to expand...
I do not understand why similar code does not work in a
multiple radio groups page.

The only difference is that in the myUnique page, I just have one
radio group; in the other page, I have 24 groups, question[0] to
question[23].

Isn't document.FORM.RADIO_GROUP_NAME an identifier for this
radio group?
Click to expand...

In that case 'FORM.RADIO_GROUP_NAME' is a name of a property of the
document object. In the context of - document.FORM.RADIO_GROUP_NAME -
it is an Identifier used in a dot notation property accessor to access
the value of the property of the document object with the
corresponding name. The equivalent bracket notation property accessor;
- document['FORM.RADIO_GROUP_NAME'] - could also be used to access the
value of the property of the document object named
'FORM.RADIO_GROUP_NAME'.

The items on each side of the dots in a dot notation property accessor
must satisfy the javascript language syntax rules that define an
Identifier, and an Identifier cannot contain square bracket
characters. But the names of the properties of objects are
unrestricted. That is, they may take forms that could not qualify as
Identifiers under the language's syntax rules. So an object may have a
property named "question[23]" but a dot notation property accessor
could never be used to access the value of that property, but a
bracket notion property accessor could because the items inside the
brackets are evaluated to strings, and string may include any
characters at all.

I think I shall be able to traverse all options by
document.FORM.RADIO_GROUP_NAME.[index] (index=1 to the length of the
radio group)
Click to expand...

No, that is a syntax error; you cannot put a dot just before an
opening square bracket in a property accessor.
 
S

SAM

Vancouver a écrit :
Hi there,

I have 24 radio button groups, and 7 options for each group. I wrote
code below trying to see if each radio button group is checked. But it
does not work. Any help? Thanks.

(24 radio button groups are named question[0] to question[23].
choices[] is to store true/false)

<script type="text/JavaScript">
function ifChecked()
{
var choices=new Array();

for (index=0;index<24;index++)
{
choices[index]=false;
for (i=0;i<7;i++)
{
if (document.forms[0].question[index].checked)
document.forms[0].elements['question['+index+']'].checked

{
choices[index]=true;
break;
Click to expand...


Why that 'break' ?
}

}
}
for (index=0;index<24;index++)
{
if (!choices[index])
{
alert ("Please make a selection");
return false;
}
}
return true;
}
</script>
Click to expand...
 
S

SAM

Vancouver a écrit :
The only difference is that in the myUnique page, I just have one
radio group; in the other page, I have 24 groups, question[0] to
question[23].
Click to expand...

yes and question[n] must be a string that's to say : "question[n]"
If not, it is an array's element ... !

and myForm.question[n] will not be correct as it is an array
(element of an array)
it is the nth+1 element of the array myForm.question

so you could use
var radioName = 'question[' + index + ']';
then calling by name
var radioCollect = document.forms[0].elements[radioName];
same as :
var radioCollect = document.forms[0].elements['question['+index+']'];
or :
var radioCollect = document.forms[0][radioName];

document.forms[0].radioName will not work
because radioName is not a real name
(it's a variable with a value)

and in collection 'radioCollect' the loop with 0<i<7 :
radioCollect
or
document.forms[0][radioName]
or, probably :
document.forms[0]['question['+index+']']


DOM way :
document.getElementsByName(radioName)
or
document.getElementsByName('question[' + index + ']')


Next time prefer names this kind : question_0, ... question_23

document.forms[0]['question_'+index]
 
D

Dr J R Stockton

In comp.lang.javascript message <e3c591a2-44a1-4097-9312-5976c85f72d7@s1
9g2000prg.googlegroups.com>, Wed, 12 Mar 2008 04:03:36, Vancouver
I have 24 radio button groups, and 7 options for each group. I wrote
code below trying to see if each radio button group is checked. But it
does not work. Any help? Thanks.
Click to expand...

I take that to mean 24 sets each of 7-way choices, with no preset
choice. Call the choices 1 to 7.

A radiobutton group can be created with no button checked, but once a
button has been checked there will always be exactly one checked in the
group.

An easy solution is to add a new, preselected, invisible Button 0.
Then, to see if one of buttons 1 - 7 is checked, just test whether
Button 0 is unchecked.
 
T

Thomas 'PointedEars' Lahn

Henry said:
[...] In practice you want to use a bracket notation property
accessor here, such as:-

document.forms[0].elements[("question["+index+"]")].checked

See:-

<URL: http://www.jibbering.com/faq/faq_notes/square_brackets.html >
Click to expand...


However, there is no need to use parentheses here. As for Pretty Printing,
they only cause less legibility instead of more. It would therefore be
better to write:

document.forms[0].elements["question[" + index + "]"].checked

or even

document.forms[0].elements[ "question[" + index + "]" ].checked

What the spaces can't do, parentheses also cannot, but syntax highlighting
in editors will.


PointedEars
 
S

SAM

Vancouver a écrit :
I managed to know why:

instead of if (document.forms[0].question[index].checked)
I need to a line like this: var name="question["+index+"]["+i+"]";,
and then: if (document.form1.name.checked)

But why? (Otherwise I get a null object) Why I cannot call
document.forms[0].question[index].checked directly?
Click to expand...


Read all the other answers !

document.forms[0].question[index]
is an element of the ARRAY :
document.forms[0].question
and not an element of the form :
document.forms[0]

the right code is (as you've seen with your var name)

document.forms[0]['question['+index+']']

document.forms[0]['question['+index+']'].checked


It is better to do :

// which collection of radio-buttons ?
var myRadio = document.forms[0]['question['+index+']'];
// loop on this collection
for(var i=0; i<myRadio.length; i++)
if(myRadio.checked) alert(i+' is checked');

to avoid to search the right collection on each pass of the loop.


This bellow works correctly.

<html>
<script type="text/javascript">

function G(){
for(var index=0; index<2; index++) {
// which collection of radio-buttons ?
var myRadio = document.forms[0]['question['+index+']'];
// loop on this collection
for(var i=0; i<myRadio.length; i++)
if(myRadio.checked)
alert('question '+(+index+1)+': response #'+(+i+1)+' is checked');
}
}

</script>
<form action="#" onsubmit="return false;">
<p>Question #1 :
<input name="question[0]" type=radio>
<input name="question[0]" type=radio>
<input name="question[0]" type=radio>
<input name="question[0]" type=radio checked>
<p>Question #2 :
<input name="question[1]" type=radio>
<input name="question[1]" type=radio checked>
<input name="question[1]" type=radio>
<input name="question[1]" type=radio>
<p>
<input type=button onclick="G()" value="go on">
</form>
</html>
 

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