NextJS Global Variable with Assignment - reactjs

Question

I'm new to NextJS, and trying to figure out, how to create a global variable that I could assign a different value anytime. Could someone give a simple example? (I know global might not be the best approach, but still I would like to know how to set up a global variable).
Let's say:
_app.js
NAME = "Ana" // GLOBAL VARIABLE
page_A.js
console.log(NAME) // "Ana"
NAME = "Ben"
page_B.js
console.log(NAME) // "Ben"

Answer 1

try using Environment Variables
/next.config.js
module.exports = {
env: {
customKey: 'my-value',
},
}
/pages/page_A.js
function Page() {
return <h1>The value of customKey is: {process.env.customKey}</h1>
}
export default Page
but you can not change its contents, except by changing it directly in next.config.js

Answer 2

Nextjs no special ways to provide global variables you want. You can achieve by:
Stateful management tool, like redux-react
Using Context

Answer 3

It's not like it's impossible,
I created a file called _customGlobals.jsx and put this as content
String.prototype.title = function () {
const sliced = this.slice(1);
return (
this.charAt(0).toUpperCase() +
(sliced.toUpperCase() === sliced ? sliced.toLowerCase() : sliced)
);
};
and imported it in _app.jsx like this:
import "./_customGlobals";
So now I can call this function on any string anywhere in my project like this:
"this is a title".title()

Answer 4

Database designed for this purpose. But for one var it's not wise to install whole db!
So, you can do it in a JSON file.
Add a var to a JSON file and use a function to update it.
this is a simple function for this usage:
const fs = require('fs');
function updateJSONFile(filePath, updates) {
fs.readFile(filePath, 'utf8', function (err, data) {
if (err) {
console.error(err);
return;
}
let json = JSON.parse(data);
for (let key in updates) {
json[key] = updates[key];
}
fs.writeFile(filePath, JSON.stringify(json, null, 2), 'utf8', function (err) {
if (err) {
console.error(err);
}
});
});
}
So, use it like this:
updateJSONFile('file.json', { name: 'John Doe', age: 30 });
You can create another function to read it dynamicly:
function readJSONFile(filePath) {
fs.readFile(filePath, 'utf8', function (err, data) {
if (err) {
return callback(err);
}
let json;
try {
json = JSON.parse(data);
} catch (error) {
return callback(error);
}
return callback(null, json);
});
}
and you can use it like this:
const readedFile = readJSONFile('file.json')
I deleted the callback function to have a simple code but you can add callback function to log error messages.