html - Javascript show/hide based on dropdown

Question

I already have the following code to show/hide two form elements based on a dropdown selection. It worked when there was a single instance of a form on the page using IDs. Now there's multiple forms, which use classes. I've tried getElementsByClass but for some reason it's not working.

Here is the Javascript:

function Toggle(obj){
    var val=obj.value;

    if (!obj.m){ obj.m=''; }
    if (!obj.m.match(val)){ obj.m+=','+val+','; }

    var hide=obj.m.split(',');

    for (var zxc0=0;zxc0<hide.length;zxc0++){
        if (document.getElementsByClassName(hide[zxc0])){
            document.getElementsByClassName(hide[zxc0]).style.display='none';
        }
    }

    var show=val.split(',');

    for (var zxc1=0;zxc1<show.length;zxc1++){
        if (document.getElementsByClassName(show[zxc1])){
            document.getElementsByClassName(show[zxc1]).style.display='';
        }
    }
}

And the HTML:

<form class="contact" name="contact" action="#" method="post">
    <label>How did you hear about us:</label>
    <div id="styled-select">
        <select name="how" onChange="Toggle(this);" class="dropdown">
            <option value="Internet Search">Internet Search</option>
            <option value="Facebook" >Facebook</option>
            <option value="Twitter" >Twitter</option>
            <option value="LinkedIN" >LinkedIN</option>
            <option value="Referral,Referral2" >Referral</option>
            <option value="Other,Other2">Other</option>
        </select>
    </div>
     <label class="Referral" style="display:none;">Referred By:</label>
     <input name="Referral2" style="display:none;" class="hidden-txt Referral2">
     <label class="Other" style="display:none;">Please Specify:</label>
     <input name="Other2" value="" style="display:none;" class="hidden-txt Other2">
     ...
</form>

When referral is selected from the dropdown, the label class=Referral and input class=Referral2 should appear. Upon selection of Other, label class=Other and input class=Other2 should appear (and referral should hide).

Answer 1

try this script just change the variables used.

<script type="text/javascript">
function ChangeDropdowns(value){
    if(value=="los"){
        document.getElementById('provider').style.display='none';
    }else if(value=="icm"){
        document.getElementById('provider').style.display='block';
    }
}
</script>

<select id="abonnement" name="abonnement" onchange="ChangeDropdowns(this.value);">
    <option value="">Selecteer soort</option>
    <option value="los">Los toestel</option>
    <option value="icm">Toestel icm abonnement</option>
</select>

<select id="provider" name="provider">
    <option value="">Selecteer een provider</option>
    <option value="">Maakt niet uit</option>
</select>