Creating Html Link Using Variable?

I'm using a form data reference, something like P-1234 for example to create a text file and a link to the file. This is during the construction of a new table or table row with javascript. I have an array of one or more references submitted via form using $_POST. On my action page I am creating a txt file P-1234. If I am creating a table ot table row using createElement(), one of the cells will have a link to the file. If the file is created as follows:

$File = $_POST['ref'][$i] . "txt";
After creating the cell
var Cell = document.createElement('td');

[code]....

I assume the link is inserted using innerHTML? If so, do I just append the filename to the end of the file path like this?

Cell.innerHTML = "http://localhost/Project/+File";