module level static data

a.mjs

const STATE = { counter: 0 };

export { STATE };

b.mjs

import { STATE } from './a.mjs';
 
export function inc() {
  STATE.counter++;
  console.log(`inc function sees static as: ${STATE.STATIC}`);
}

index.mjs

import { STATE } from './a.mjs';
import { inc } from './b.mjs';
 
console.log(STATE); // { counter: 0 }
 
inc();
console.log(`inc() bumped counter to ${STATE.counter}`);
 
Object.defineProperty(STATE, "STATIC", {
  enumerable: true, // so we can see it in console.log
  writable: false,
  value: 'my static data'
});
 
inc();
console.log(`inc() bumped counter to ${STATE.counter}`);
 
try {
  STATE.STATIC = "will throw";
} catch {
  console.log("Hey it threw");
}

output.log

$ node index.mjs 
{ counter: 0 }
inc function sees static as: undefined
inc() bumped counter to 1
inc function sees static as: my static data
inc() bumped counter to 2
Hey it threw