Where to store the value of a variable for node.js to access it permanently?

Question

Node.js

There is a script which can be executed very long. It is necessary during its operation to write down a variable somewhere so that you can refer to it from another request. (track progress)
For example:

app.post('/one', (req, res) => {
var i = 146
console.log(i) -146
}

app.post('/two', (req, res) => {
console.log(i) -146
}

I do not want to use the database, it does not work in files either.
I'm thinking of storing it in RAM, but I don't know how to write data to it (also with the ability to read, delete, overwrite) .
Or is it generally worth using sockets for such purposes and not soaring the brain? Hence the question:
what will load the server more -
executing a post request (read such a variable - give a value) every 3-5 seconds or an open socket channel?

Answer 1

Key-value storage: memcached, Redis for these tasks. and you need to start using Websockets when you need to start receiving events from the server