Javascript - Populate 2 textbox with 1 select list

Sorry but your example has only one texarea...

However if I don't' have misunderstood your question you can simply do that:

var mytextbox = document.getElementById('mytext');
var mytextbox2 = document.getElementById('mytext2');

var mydropdown = document.getElementById('dropdown');

mydropdown.onchange = function(){

   mytextbox.value = mytextbox.value  + this.value;
   mytextbox2.value = mytextbox2.value  + this.value;
}

<textarea id="mytext"></textarea>
<textarea id="mytext2"></textarea>
<select id="dropdown">
<option value="">None</option>
<option value="contactnumber1">text1</option>
<option value="contactnumber2">text2</option>
<option value="contactnumber3">text3</option>
<option value="contactnumber4">text4</option>
</select>

var mytextbox = document.getElementById('mytext');
var mytextbox2 = document.getElementById('mytext2');
var mydropdown = document.getElementById('dropdown');

mydropdown.onchange = function () {
mytextbox.value = mydropdown.options[this.selectedIndex].text;
mytextbox2.value = mydropdown.options[this.selectedIndex].value;
};

do you mean, you want to append selection each time some body selects item from drop down? I do not see two text boxes in your fiddle that is why I am asking...

if you want unique values selected then..

var mytextbox = document.getElementById('mytext');
var mydropdown = document.getElementById('dropdown');
var strValue =  new String();
mydropdown.onchange = function(){
if(strValue.indexOf(this.value)<=0){
   if(strValue!="")
{
    strValue += "," + this.value;
}
else
{
    strValue = this.value
}
}
mytextbox.value = strValue;
}

So you are wanting two values to be populated by one tag. With that said, what if you just put data attributes in the option tag? data-contactNumber data-longName

<select>  
<option value="x" data-contactNumber = "yyyy" data-longName="zzzz">  
.....
</select>  

Then you can just assign the selected option text boxes the individual data attrs??