checking and unckecking a checkbox

[Willie]

I have a script that I want to check the checkbox if something is writen in
a text field. Then uncheck it if it erased.
The check works but not the uncheck.
Here is the code:
String.prototype.trim =
function()
{
return this.replace(/^\s+|\s+$/g,'');
}
function mark(fn, textfield, checkbox){
var check = (document.forms[fn][checkbox]);
var text = (document.forms[fn][textfield]);

text = text.value.trim();
if(text.value != ""){
checkbox.checked = 'true';
}
if(text.value == ""){
checkbox.checked = 'false';
}
}

in the form :
<input type="text" name="RepID"
onChange="mark('f1','RepID',this.form.checkbox)">

 

[Martin Honnen]

checkbox.checked = 'true';
}
if(text.value == ""){
checkbox.checked = 'false';

checked is a boolean property so you should assign boolean values not
strings e.g.
checkbox.checked = true;
or
checkbox.checked = false;

 

[Willie]

Thanks, that was simple.

checked is a boolean property so you should assign boolean values not
strings e.g.
checkbox.checked = true;
or
checkbox.checked = false;

 

[Doug Miller]

text = text.value.trim();
if(text.value != ""){
checkbox.checked = 'true';
}
if(text.value == ""){
checkbox.checked = 'false';
}

'true' and 'false' are strings. <element>.checked is a Boolean property. Any
non-null string, when interpreted as Boolean, is true; only the null string ""
is false. Thus when you assign the value 'false' to checkbox.checked, it
receives the Boolean value true.

Also, your second 'if' is pointless; simpler is

if (text.value != "") {
checkbox.checked = true;
} else {
checkbox.checked = false;
}

or, simpler still,

checkbox.checked = (text.value != "");

 

[Dr J R Stockton]

I have a script that I want to check the checkbox if something is writen in
a text field. Then uncheck it if it erased.
The check works but not the uncheck.
Here is the code:
String.prototype.trim =
function()
{
return this.replace(/^\s+|\s+$/g,'');
}

Not needed.

function mark(fn, textfield, checkbox){
var check = (document.forms[fn][checkbox]);
var text = (document.forms[fn][textfield]);

check.checked = /\S/.test(text.value)
}

It will be checked if a non-whitespace character is found in the string;
otherwise cleared.

It's a good idea to read the newsgroup c.l.j and its FAQ. See below.

 

[Tim Streater]

can js do something like:

checkbox.checked = (text.value == "");

Yes but personally I find such constructs to be unreadable; I spend 30
mins figuring out what it means. I would put:

checkbox.checked = true;
if (text.value == "") checkbox.checked = false;

This is because I have a simple mind. I am not impressed by the
programmer being a smartypants. I am impressed by neat and logical
layout that allows you to figure out quickly what is going on. Useful
when it comes to maintaining someone else's code.

 

[Tim Streater]

It is.

Well, if it's only into the harbor we're probably OK. If he throws it
into the harbour, on the other hand, then we're in trouble.

 

[David Cox]

checked is a boolean property so you should assign boolean values not
strings e.g.
checkbox.checked = true;
or
checkbox.checked = false;

can js do something like:

checkbox.checked = (text.value == "");

?
David F. Cox

 

[Doug Miller]

can js do something like:

checkbox.checked = (text.value == "");

Yes, it can. See my earlier post in this thread. What the OP wants in this
case, though, is

checkbox.checked = (text.value != "");

 

[David Cox]

'true' and 'false' are strings. <element>.checked is a Boolean property.
Any
non-null string, when interpreted as Boolean, is true; only the null
string ""
is false. Thus when you assign the value 'false' to checkbox.checked, it
receives the Boolean value true.

Also, your second 'if' is pointless; simpler is

if (text.value != "") {
checkbox.checked = true;
} else {
checkbox.checked = false;
}

or, simpler still,

checkbox.checked = (text.value != "");

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

It is.

I must read the entire thread before posting.

I must read the FAQ before posting.

I must read my own post before posting.

I must remember I said all that last time. :-<

David F. Cox