ExpressJS - Small curiosity - express

Question

My thing is a small project.
In main what it does is that the "server" will get a call from the link directly what will run some functions that will update the database and the data that has to be shown.
I will show what I mean:
function updateData(){
connection.query(`SELECT * FROM muzica WHERE melodie = "${updateList()}"`, function (error, rezultat, fields) {
if (error) {console.log('err la selectare')};
//express output
let data = {
melodie: rezultat[0].melodie,
likes: rezultat[0].likes
}
console.log(data.likes);
app.get('/like', (req,res) =>{
res.json(`${data.likes}`);
});
}
setInterval(()=>{
updateData();
}, 20000)
Uhh, how to explain it, I'm so bad at this...
So, in main, I'm new to back-end work, everything that I did was based on their Documentation as I learn way faster by my needs than some guides and so on.
So, when I or someone does my http://website/like it should show just data.likes, cause that is all that I need, don't count data.melodie (i will clean that later on) after I finish all the code.
Anyway, whenever I do website/like data.likes is not updating to the new database data.likes.
For example, data.likes before were 5, in a few minutes it can be 2 but whenever I call website/like show "5" than its new value 2.
Don't be hash on me, I'm new and I want to learn as much as I can, but I can't understand the above case, by my logic it should ALWAYS show what its in database when it refreshes each 10 seconds(I run this in localhost so I will not stress any online server).
But if there is any better way to check for databases update than "setInterval" please notice me.
It's hard to learn alone without a mentor or someone else to talk about this domain.
Thank you for your time!
Kind regards,
Pulsy

Answer 1

You have things a bit inside out. A request handler such as app.get('/like', ...) goes at the top level and you only ever call it once. What that statement does is register an event handler for any incoming requests with the /like path. When the server receives an incoming request for /like, it will then call the function for this route handler.
You then put inside that route handler the code that you want to run to generate the response and send the response back to the client.
app.get('/like', (req, res) => {
connection.query(`SELECT * FROM muzica WHERE melodie = "${updateList()}"`, function (error, rezultat, fields) {
if (error) {
console.log(error);
res.sendStatus(500);
} else {
//express output
let data = {
melodie: rezultat[0].melodie,
likes: rezultat[0].likes
}
res.json(data);
}
});
});

Answer 2

The endpoints need to be outside of any functions in express.
For example, if you look at the express "hello world" example here, you will see that they have a basic app that only has a single GET endpoint defined which is "/" so you would access it by running "localhost/" or "127.0.0.1/".
In your case, you want your endpoint to be "/like", so you must define something like:
const express = require('express')
const app = express()
const port = 3000
app.listen(port, () => console.log(`Example app listening at http://localhost:${port}`))
app.get('/like', (req, res) => {
// do database stuff and assign data variable
// res.json(data);
}