checking multiple checkboxes at once?

[jazztie]

I have the following problem...

I have a list of names with checkboxes in front of them. The list is generated from a database.
So in a loop it would look something like this:

<input type=checkbox value='$userID' name='recipients[]'> $UserName

The name of the checkbox is a Array, because I want to pass the information on to another page, where the emails-addresses are used to send a mail.

the userID is also linked with the email-account of the user. What I want to do is to have a link, button or checkbox (which one is the easiest to implement) that checks all the checkboxes in the list at once. How do I go about this?

I have come up with the following, but this doesn't seem to work:

function CheckEm(cb_mail){
  for (var i = 0; i < document.myForm[cb_mail].length; i++)
    document.myForm[cb_mail][i].checked = true;
}

<input type=checkbox onClick="CheckEm('cb_mail')"> 

Can some help with this one? All help will be greatly appreciated

Jazz

[Anarchos]

Wow you came up with that yourself? Good work.

[jazztie]

Sorry Anarchos, you're right, you posted it first... I changed to question a bit while trying.

The function I use now is:

    <!--
        function CheckEm(recipients){
        if (document.mailer.cb_all.checked == true){
          for (var i = 0; i < document.mailer[recipients[]].length; i++)
            document.mailer[recipients][i].checked = true;
        }
        else {
          for (var i = 0; i < document.mailer[recipients[]].length; i++)
            document.mailer[recipients][i].checked = false;
        }
    }
    //--> 

and in the form it reads:

<form name='mailer' method='POST' action='mail_multiple_1.php'>
    <input type=checkbox name='cb_all' onClick=\"CheckEm('recipients')\"><br>

$RelationQuery    = mysql_query("SELECT * FROM relation");
if(mysql_num_rows($RelationQuery) > 0) {
  while ($rows    = mysql_fetch_array($RelationQuery)){
      extract($rows);
    print "<tr><td><input type=checkbox value='$rid' name='recipients[]'>$firstName $lastName</td><td>$email</td></tr>";
  }
} 

I get an error, reading that 'Object is expected'.
What am I doing wrong?

PS: thanks goes out to Anarchos for writing the first part of the code!!!

[Anarchos]

No problem, here's some code that works:
<script type="text/javascript">
<!--
function checkEm(elm,name){
for (var i = 0; i < elm.form[name].length; i++)
elm.form[name][i].checked = elm.checked;
}
//-->
</script>
<form>
<input type="checkbox" name="blah" />
<input type="checkbox" name="blah" />
<input type="checkbox" name="blah" />
click <input type="checkbox" name="blah2" onClick="checkEm(this,'blah')" />
</form>

[Anarchos]

Here's a better version:

function checkAll(elm,name){
  for (var i = 0; i < elm.form.elements.length; i++)
  	if (elm.form.elements[i].name.indexOf(name) == 0)
	    elm.form.elements[i].checked = elm.checked;
}

It'll check all elements whose name begins with name. So you can do blah1, blah2, blah3, and it'll check em all if you do checkAll(this,'blah')