Re-"res.render" URL after "fetch POST"-ing DOM data array to Node-js

Even after reading many related questions, I am uncertain as to what exactly is the best approach to render a URL after JS frontend collects DOM data and fetch POSTs it to an express server POST URL.

• I am aware of the fact that fetch POST does not ask for rendering
• at this point I am not asking for an alternative POST method (XML / FORM etc.). I would ask a seperate question if this current approach is not valid
• I am thankful for replies on how to instantly "refresh" the URL as well, this is however predominantly asking about having the URL rendered for the next browser GET request
• I am "presuming" to understand that my app only renders the URL once at server start and that this is the problem

How can I call the function render after the fetch POST and the MYSQL query "ttupdate" have completed?

// snippet render code ////////////////////////////////////////////////
function render(file, url, contentdata) {
    app.get(url, async(_req, res, next) => {
        try {
            res.render(file, { data: await contentdata });
        } catch (err) {
            next(err);
        }
    });
}


render('time-picker', '/time-picker', timetablesthree)

Where and how in the following snippet would you implement it?

// snippet new TIME-PICKER table to DB 
app.post("/time-picker-input", async(req, res) => {    
   
    for(i=0; i<=167; i++) {        
        let inputFieldId = req.body[i].fieldid;
        let inputFieldValue = req.body[i].fieldvalue;
        // console.log(inputFieldId);  

    await ttupdate(inputFieldValue, inputFieldId, 'timetablesthree');
    };
    res.json({ message: 'Success' });
 });

Additional information on my setup:

let express = require('express')
let bodyParser = require('body-parser')
let app = express()
app.set('view engine', 'ejs')
let path = require('path')
app.set('views', path.join(__dirname, 'views'))
app.use(express.static(path.join(__dirname, 'public')));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({
    extended: true
}))
app.use((err, req, res, next) => {
    console.error(err.stack)
    res.status(500).send('Sorry - something broke...')
})
app.listen(3000, (req, res) => {
    console.log("App is running on port 3000")
})

let { singledbentry, refresh, refreshTwo, ttupdate } = require("./database.js")
let activetime = require('./activetime.js');

let mysql = require('mysql2')

It was a matter of variable scope.

Background: A lot of endpoints rendered correctly and also rendered correctly with updated data after a FORM action POST.

The only endpoint not rendering properly, unless after server restart, was using fetch POST. So I was mislead to believing the obvious cause to be the different behavior of fetch POST (like not requesting rendering like a browser).

However none of the endpoints rendered correctly after reloads. This was just not visible, as they always displayed the correct data through express POST res.render.

Edit:

For future readers: I took the route out of the function and passed the information for "timetablesthree" directly to prove that is was an issue of variable scope.

The following code works fine:

app.get('/time-picker', async(_req, res, next) => {
    try {
        timetablesthree = refresh('SELECT ttfield, ttfieldvalue FROM timetablesthree')
        res.render('time-picker', { data: await timetablesthree });
        console.log(timetablesthree);
    } catch (err) {
        next(err);
    }
});