Closures manipulate variables directly (but they have to be spelled right!)

closure.js

'use strict';

function scope() {
  var i = 0;
  var s = "original";
  var b = true;
  var o = { field: 0 };
  return {
    inc: function () { i++; },
    reset: function () { i = 42; },
    get: () => i,

    // had a lot of trouble when my string var was called 'princess' and the function assigned to 'princes'. 
    // that's why we absolutely always need 'use strict'!
    resetString: function () { s = "changed"; },
    getString: () => s,

    resetBool: function () { b = false; },
    getBool: () => b,

    resetObject: function () { o = { noField: 0 }; },
    getObject: () => o,
  }
}

function main() {
  const blackbox = scope();

  console.log("numbers and booleans are passed as variables");

  console.log(blackbox.get());

  blackbox.inc();
  console.log(blackbox.get());

  blackbox.reset();
  console.log(blackbox.get());

  console.log(blackbox.getBool());
  blackbox.resetBool();
  console.log(blackbox.getBool());

  console.log("(references to) strings and objects are also passed as variables");

  console.log(blackbox.getString());
  blackbox.resetString();
  console.log(blackbox.getString());

  console.log(blackbox.getObject());
  blackbox.resetObject();
  console.log(blackbox.getObject());
}

main();