Populate a text field from a dropdown field?

I'm very new to Javascript..!

I need to populate a text field (subject) based on a dropdown field (new_etape) when the user changes the value in that field.

Let's say the user selects a value in the dropdown, I need to send that value to the 'subject' field.

I think I'm pretty close but I also think I'm missing a part where I need to convert the dropdown value to text. Or maybe I'm way off track.

Here is my code:

function updatesubject () { 

var etape = Xrm.Page.getAttribute('new_etape').getValue();

if(etape==null)return;

var result = etape;

Xrm.Page.getAttribute('subject').setValue(result);

}

Any advice?