.push() isn't saving to my array - NodeJS - node.js

Question

I'm trying to code a Webserver in plain NodeJS with http. What i'm trying to do is when you have the url /add/ whatever is after the /add/ would be added to a array, and showen on / but its not saving the array, and resets it when i add something new. Can someone explain what i did wrong?
Sorry that my code is a bit messy.
Index.js:
const http = require('http');
const $conf = require('./config.json');
http.createServer((req, res) => {
let $list = [];
const url = req.url;
const $req = url.split('/');
const $req_q = url.split('?');
if (req.url == "/"){
res.write($list.toString());
} else if (req.url == `/add/${$req[2]}`){
$list.push($req[2])
console.log($list)
res.write(`ADDED ${$req[2]}`)
} else {
res.write('Error');
}
res.end();
}).listen($conf.port);
Config.json:
{
"port": 80
}
When i goto /add/hi
i get "ADDED hi".
Then go back to /
and get nothing.

Answer 1

A NodeJS webserver executes a route (e.g '/' or '/add') on-demand. That means that everything inside the function is executed from scratch on every request.
Therefore your $list variable gets initialized everytime you call a route and you can't see the result on the screen.
You can fix it by moving the variable to the global scope.
const http = require('http');
const $conf = require('./config.json');
let $list = []; // Now this value is persisted between requests
http.createServer((req, res) => {
const url = req.url;
const $req = url.split('/');
const $req_q = url.split('?');
if (req.url == "/"){
res.write($list.toString());
} else if (req.url == `/add/${$req[2]}`){
$list.push($req[2])
console.log($list)
res.write(`ADDED ${$req[2]}`)
} else {
res.write('Error');
}
res.end();
}).listen($conf.port);

Answer 2

The main reason is the $list array is initialized every time there is a new request. So, there can be two ways of doing this at the moment.
Create a variable outside this route scope so you can access the previous value. (this variable will be shared for every request/client)
Another and more efficient way is you can store the value more efficiently using node-json-db, as there might be thousands of request for which you might need to save this data and it won't be efficient at that time. You can use node-json-db.
Sample code:
import { JsonDB } from 'node-json-db';
import { Config } from 'node-json-db/dist/lib/JsonDBConfig'
// The first argument is the database filename. If no extension, '.json' is assumed and automatically added.
// The second argument is used to tell the DB to save after each push
// If you put false, you'll have to call the save() method.
// The third argument is to ask JsonDB to save the database in an human readable format. (default false)
// The last argument is the separator. By default it's slash (/)
var db = new JsonDB(new Config("myDataBase", true, false, '/'));
// Pushing the data into the database
// With the wanted DataPath
// By default the push will override the old value
db.push("/test1","super test");
// Get the data from the root
var data = db.getData("/");
// From a particular DataPath
var data = db.getData("/test1");
// If you try to get some data from a DataPath that doesn't exists
// You'll get an Error
try {
var data = db.getData("/test1/test/dont/work");
} catch(error) {
// The error will tell you where the DataPath stopped. In this case test1
// Since /test1/test does't exist.
console.error(error);
};
There are several other operations you can perform for that you should check its documentation.