It searched and already included the typical backend code

app.use(function (req, res, next) {
    //res.setHeader('Access-Control-Allow-Origin', 'http://localhost:3000/storeScore');
    res.header('Access-Control-Allow-Origin', '*');
    //res.header('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT, PATCH, DELETE');
    res.header('Access-Control-Allow-Methods', 'GET, POST, OPTIONS');
    res.header('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept');
    next();
});

but I still get Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://localhost:3000/storeScore. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing). followed by

Uncaught (in promise) TypeError: NetworkError when attempting to fetch resource. I mean don't I have the header res.header('Access-Control-Allow-Origin', '*'); ?

My frontend code is

function someFunction() {
            const sessionHighscore = cumulativeScore;
            const options = {
                method: 'POST',
                headers: {
                    //'Origin' : 'http://localhost:80',
                    'Content-Type': 'application/json'
                },
                body: JSON.stringify(sessionHighscore)
            };

            fetch('http://localhost:3000/storeScore', options);
        }

Maybe I need to include something in client-side header? I think local html is hosted on port 80?

Notes:

• I am trying to send data from a local website to a mysql database on localhost:3000
• I am using express for backend, and trying Not to use cors module as solution
• Also is there any resources to show me how to execute routes without manually changing localhost? Like to use localHost:3000/createTable I have to type this manually into the url, can I do this with code?

Edit:

• Looking at network tab in my browser I found the OPTIONS request is successful but the POST after is missing the 'Access-Control-Allow-Origin' header; I just need to know to how to ensure the POST also gets the header