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multiple-select form validation with javascript

dear mr helpman,

i use js to validate a html form. all works well except when i try to check if any one option of a multiple select element has been selected (none selected by default). i really don't know how to address the element in js.

the following code works for text boxes, but not for my multiple=multiple element.

Code:

function kontakt_validate() {

if(document.Formular.field.value == "") {

        alert("not like this);

document.Formular.field.focus();

        return false;

}

any help would by much appriciated,

"baikonur"

Hi

For multiple selects, you need to go thru all the options and check if they are selected or not. Here is an example:

[HTML]<script type="text/javascript">
function verify(myform) {
var sel = myform.mySelect;
var num = 0;
for ( var i=0 ; i<sel.options.length ; i++ )
if (sel.options[i].selected)
num++;
if (!num) {
alert("Select some numbers please");
sel.focus();
return false;
}
return true;
}
</script>
<form action="#" method="post" onSubmit="return verify(this);">
<select name="mySelect" multiple>
<option value=1>One</option>
<option value=2>Two</option>
<option value=3>Three</option>
</select>
<input type="submit">
</form>[/HTML]

Hello Guttorm,

thanks for your help.
however, i can't get it to work.
since i use js only for validation, i am always in big trouble if code doesn't work as expected. maybe you can have a 2nd look?
this is the releveant part of the html/php file:

Code:

                        <select id="wideselec" name="Leistungen[]" size="8" multiple="multiple">

                        <option value="Beratung zur materiellen Existenzsicherung">Beratung zur materiellen Existenzsicherung</option>

                        <option value="Beratung bei Schulden">Beratung bei Schulden</option>

it's necessary in my case to append [] at the end of the name, to be able to handle the array in php. could that be a problem?

this now is how i used your example:

Code:

function kontakt_validate(myform) {

        var sel = myform.Leistungen;

        var num = 0;

        alert("hallo");

        for ( var i=0 ; i<sel.options.length ; i++ )

                if (sel.options[i].selected)

                        num++;

        if (!num) {

                alert("Select some numbers please");

                sel.focus();

                return false;

        }

        else {

                alert("boo");

                }

        return true;

}

it doesn't pop up, also setting sel to "document.Formular.Leistungen[]" doesn't help... the code isn't even parsed after that line if i put it like that. (i know that from putting in those alert boxes... sadly enough the only means of "debugging" i know in js) so i assume the square brackets don't belong here in js.
neither one of the alert boxes in "if" or "else" have ever been executed.

ok, it's definetely the name of the multiple field that causes me trouble. if i print the value of the variable "sel" in an alert box i get an "undefined". when trying that with a normal select box i get [object HTMLSelectElement]...
so i guess the square brackets are my problem...

Yes, when the name contains [], you can't reference it in Javascript that way. But I see you have an id in the select tag - "id="wideselec".

This won't work:
var sel = myform.Leistungen;

I think this will:
var sel = document.getElementById('wideselec');

Quote:

Originally Posted by Guttorm (Post 2921777)

I think this will:
var sel = document.getElementById('wideselec');

it does!! thank you very much, Guttorm! :)
i'd like to ask one last question, if you don't mind: can you recommend a good online resource for learning javascript. i know my way around bash, php, html and css quite well, have also peeked into python and had to study c++ at one point. except for c++, i found that for those languages there is better material available for study online than in books. is it like that with js, too?

thanks again!

baik

Glad to help.

As for studying Javascript, I read the book "Javascript - The definite Guide" by O'Reilly, and I think it's a very good book. It's a bit old now, but I haven't seen anything better. I've seen lots of references online, but no real good tutorial. Maybe someone else knows?

For a language reference site, I like www.gotapi.com. It covers a lot of different languages, including javascript.

yes, language reference is available online, but no good tutorial indeed. thanks for the book recommendation, however... i'll get that one then. (matter of fact, i had it in my hands yesterday when i was in the book store... i was discouraged by its enourmous size, must be 1000 pages or something. well ok, if that is the K&R for javascript, so be it! maybe i'll start using js for more than just validation in the future.)

:)

baik