Q:

How can I easily handle redirects by JSON in HTML/JavaScript? 

I have a directory on my web server called /go/. In practice, this would be used as https://example.com/go/x where x is a variable stored in a JSON file.  The JSON file can be set up like so;
{
    "stackoverflow": "https://stackoverflow.com/",
    "apple":         "https://apple.com/",
    ...
}

I would like to, somehow, check if any of these variables check the /go/x and redirect them to their equivalent.  In practice, it would be used like https://example.com/go/stackoverflow and it will redirect me to this site. 
I don't want to add multiple HTML files in that directory and redirect from there, as I want to externally manage the JSON responses.  That is irrelevant though. 
I currently don't already have a solution, but was thinking of a JavaScript script that checks the JSON for any match.  I don't know, however, how that script will get run because it never gets hit or called by anything.  I already have the script that could get called, but don't know how to call it when /go/x is urgent:
import "Paths.json" as Paths;
if (window.location.pathname == "/go/") {
    const Location = JSON.parse(Paths)[window.location.href];
    window.location.replace(Location);
}

Conclusion: I would like to redirect users to different pages depending on the variable x in /go/x. The redirects are stored in JSON.  Every time /go/ gets hit, I would like to run a JavaScript script to check on that variable and redirect the user to another page without adding different HTML files for each redirect and so forth. 

A:

You could configure your web server to serve a html file, say redirect.html for /go/*.  This preserves the pathname while handling all paths
You could then redirect the user based on the pathname. 
Script in redirect.html:
const data = //load data;
const redir = location.pathname.replace("/go/","");
location.href = data[redir];

