Manage value from a global variable NextJs

I have 2 routes (example1 and example2), I want to have a global general variable that can be accessible by these 2 routes.

One example:

//api/variable.ts
let test = 0

//api/example1.ts

setTest =() => {
  test=2
}

//api/example2.ts

getTest =() => {
  return test
}

Now I want to call some routes and the value of the variable should be updated

// mainFile.ts

setTest()
getTest() // It should return 2, but it returns 0

How could I create a global variable like that? I tried to use a singleton class just for this variable, but it didn't work.