Append dropdown list result to formData object - php

Question

In html I have a file input element within a form:
<input type="file" id="file-select" name="photos" />
Then in javascript I append this to my formData object (formData) as follows:
formData.append('photos', file, file.name);
Then finally in php I retrieve the transferred file.
$fileName = $_FILES['photos']['name'];
This works great.
However I also have a dropdown list in the same form in HTML:
<label>Select Year to Load File to:</label>
<SELECT name = "year_list">
<OPTION Value="2013">2013</OPTION>
<OPTION Value="2014">2014</OPTION>
<OPTION Value="2015">2015</OPTION>
<OPTION Value="2016">2016</OPTION>
</SELECT>
However it is not clear to me what the syntax I need to use to append the users selection to formData and also to retrieve the result in php. Can someone enlighten me as to how to do this?
I Do not want to use jquery.
I understand for the append statement I should use the syntax:
append(DOMString name, DOMString value);
But then what DOMString name and DOMString value would I use? And what would I use in $_POST in the php file?
Many thanks.

Answer 1

Thanks folks. After a bit of sleep and some further experimentation I got it to work as follows:
In javascript declared variables to get the values from the dropdown list and appended those values to the formData object as follows:
var sel_month_list = document.getElementById("month_list");
var month_list = sel_month_list.value;
var sel_year_list = document.getElementById("year_list");
var year_list = sel_year_list.value;
formData.append('month_list', month_list);
formData.append('year_list', year_list);
Then in php the following successfully retrieved the values:
$month = $_POST['month_list'];
$year = $_POST['year_list'];
Seems a little cumbersome but it worked. Feel free to pitch in if there is a more elegant way to achieve this.
Regards