How to fill and add text in a text field with drop down selections

I'm not a coder ut I've found this code here

http://ift.tt/17c3aZ2

<textarea id="mytext"></textarea>

<select id="dropdown">
    <option value="">None</option>
    <option value="text1">text1</option>
    <option value="text2">text2</option>
    <option value="text3">text3</option>
    <option value="text4">text4</option>
</select>

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

mydropdown.onchange = function(){
     mytextbox.value = mytextbox.value  + this.value;
}

I'd like to modify it so that I've more than one dropdown and each one add his text in the same field.

Practically I'd have to create a compact code easily for the user so that the user select some phrases using the dropdown and the code will fill the text field.

If I can be more precise please let me know. As said Iìm not a coder so if you can write down the code to use I'll be very happy.

Thanks!