jquery - Executing PHP code inside a .js file

I'm trying to get a bit of PHP to execute inside of a .js file, but obviously don't know how to do it properly.

Basically the code is adding some HTML tags to my page, which I am using for a slideout contact form. However the contact form itself is done in Wordpress by a shortcode. So I'm trying to get the shortcode to work inside the code that makes the form slide out.

var phpTest = '';

// add feedback box
$this.html('
'
    + thisSettings.title
    + '
'
    + phpTest
    + '
');

If I change the variable "phpTest" to a regular string with text, it shows up fine, I'm just not sure how to execute the php in this instance.