Input to Javascript from file via php

I have a setup where I want to send the results of a python script asynchronously to a webpage. I currently have a HTML page setup, with a Javascript file that deals with the information dynamically.

However, I don't really understand how to get the Javascript to interact with Server-side files, seeing as its done through PHP. What do I do to set up a php file that takes the input from a text file (generated every x seconds from the python script), and sends it to the Javascript?

via Chebli Mohamed