Read local text file using Javascript

Question

I am following an old stackoverflow post on how to read in a text file using javascript seen here: Javascript - read local text file and I cannot get it to work. I am very new to javascript and all I want to do is store the file to a var and display it on screen so I know it is being read in and split correctly. What am I doing wrong? I know there are many new ways to do this but this is a very early attempt at javascript for me and I found this code to be the most readable example I found online. Im not sure if it matters but the file im trying to read from is about 300 pages of gps data.

I tried:

pasting the file path into my browser (works fine)

removing the state and status checks (no difference.... and bad practice I know)

changing browsers (no difference, though I have been using Chrome)

var allText;

function readTextFile(file)
{
var rawFile = new XMLHttpRequest();
rawFile.open("GET", file, false);
rawFile.onreadystatechange = function ()
{
    if(rawFile.readyState === 4)
    {
        if(rawFile.status === 200 || rawFile.status == 0)
        {
            allText = rawFile.responseText;
            alert(allText);
        }
    }
}
rawFile.send(null);
}
readTextFile("file:////var/www/html/gpsPoints.txt");
locations=allText.split(",");